Composite spot coating slurry as well as preparation method and application thereof

Abstract

The invention discloses composite point coating slurry and a preparation method and application thereof.The composite point coating film comprises a base film and a coating on the base film, the coating is obtained by coating the composite point coating slurry, and the method for preparing the composite point coating slurry comprises the steps that ceramic slurry and organic slurry are mixed to be uniform to obtain the composite point coating slurry, the ceramic slurry comprises a ceramic material, the organic slurry comprises an organic material, the ceramic material comprises a first dispersant, ceramic powder, a wetting agent, a first thickening agent and a first binder, and the organic material comprises a second dispersant, an organic polymer, a second thickening agent and a second binder. The composite spot-coating slurry and the matrix arrangement of the spot-coated coating points are cooperated to reduce the risk that the particles block the holes, the air permeability of the diaphragm is improved, and the internal resistance of the lithium battery is reduced.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a composite dot-coating slurry, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) are characterized by high voltage, high specific energy, and high cycle efficiency, and are widely used in various fields of production and daily life. Among them, the separator, as an indispensable part of lithium-ion batteries, plays an important role in the safety and electrochemical performance of lithium-ion batteries.

[0003] Wetting properties, heat resistance, and adhesion are important parameters for evaluating lithium-ion battery separators. For example, the invention patent with publication number CN109065805A improves the wettability of the separator by preparing a polymer coating with high liquid absorption rate. However, this method uses low crystallinity polymer powder, which does not improve the mechanical and thermal stability of the separator. The invention patent with publication number CN111129405A uses a mixed coating separator slurry. Although this patent improves the heat resistance of the separator, the interface effect is not good, causing the battery capacity retention rate to drop by 5% after only 100 cycles. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a composite dot coating film.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned composite dot-coated film.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] A composite dot-coated film includes: a base film and a coating layer on the base film, wherein the coating layer is obtained by coating with a composite dot-coating slurry. The method for preparing the composite dot-coating slurry includes: mixing a ceramic slurry and an organic slurry until homogeneous to obtain the composite dot-coating slurry, wherein the ceramic slurry includes: ceramic material and a first water, and the organic slurry includes: organic material and a second water, wherein the ratio of ceramic material in the ceramic slurry to organic material in the organic slurry is (0.1~20):1 by mass parts.

[0008] The ceramic material includes: a first dispersant, ceramic powder, a wetting agent, a first thickener, and a first binder; the organic material includes: a second dispersant, an organic polymer, a second thickener, and a second binder.

[0009] In the above technical solution, the solid content of the ceramic slurry is 25~36wt%, and the solid content of the organic slurry is 15~20wt%.

[0010] In the above technical solution, the ratio of the first dispersant, ceramic powder, wetting agent, first thickener and first binder in the ceramic material by mass parts is (0.4~0.8):(28~36):(2~8):(5~9):(1~5).

[0011] In the above technical solution, the ratio of the second dispersant, the organic polymer, the second thickener and the second binder in the organic material by mass parts is (0.1~0.5):(17~20):(8~12):(7~11).

[0012] In the above technical solution, the first thickener is a cellulose-based thickener.

[0013] In the above technical solution, the second thickener is a cellulose-based thickener.

[0014] In the above technical solution, the cellulose thickener includes one or a mixture of several of sodium carboxymethyl cellulose, carboxymethyl hydroxypropyl cellulose, and hydroxyethyl cellulose.

[0015] In the above technical solution, the first adhesive includes: polyacrylate.

[0016] In the above technical solution, the second adhesive includes: polyacrylic acid.

[0017] In the above technical solution, the organic polymer is one or a mixture of several of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, tetrafluoroethylene-vinylidene fluoride copolymer, and polymethyl methacrylate.

[0018] In the above technical solution, the ceramic powder is one or a mixture of several of alumina, boehmite, silicon dioxide, titanium dioxide, calcium oxide, calcium carbonate, calcium titanate, and barium titanate; preferably boehmite or alumina.

[0019] In the above technical solution, the first dispersant is one or a mixture of several of the following: cationic ammonium salt dispersants, acrylate polymeric dispersants, polyurethane polymeric dispersants, and polyester polymeric dispersants.

[0020] In the above technical solution, the second dispersant is one or a mixture of several of the following: cationic ammonium salt dispersants, acrylate polymeric dispersants, polyurethane polymeric dispersants, and polyester polymeric dispersants.

[0021] In the above technical solution, the wetting agent is one or a mixture of several of the following: nonionic surfactants, organosilicon nonionic surfactants, and anionic surfactants.

[0022] In the above technical solutions, the nonionic surfactant is polyoxyethylene octylphenol ether or polyoxyethylene lauryl ether; the organosilicon nonionic surfactant is polyether-modified dimethyl polysiloxane; and the anionic surfactant is sodium dodecylbenzene sulfonate or sodium fatty alcohol polyoxyethylene ether sulfate.

[0023] In the above technical solution, the particle size of the ceramic powder is D50: 0.1~0.5μm, D90: 0.4~0.8μm, and D99: 0.5~1.3μm.

[0024] In the above technical solution, the method for preparing the ceramic slurry includes: mixing a first water and a first dispersant, stirring until uniform, then adding ceramic powder, stirring until uniform, and finally adding a wetting agent, a first thickener and a first binder, stirring until uniform to obtain a ceramic slurry. The ratio of the first dispersant, ceramic powder, wetting agent, first thickener and first binder by mass parts is (0.4~0.8):(28~36):(2~8):(5~9):(1~5).

[0025] The method for preparing the organic slurry includes: mixing the second water and the second dispersant, stirring until uniform, then adding the organic polymer, stirring until uniform, and finally adding the second thickener and the second binder, stirring until uniform to obtain the organic slurry. The ratio of the second dispersant, the organic polymer, the second thickener and the second binder by mass parts is (0.1~0.5):(17~20):(8~12):(7~11).

[0026] In the above technical solution, the viscosity of the ceramic slurry is 35~95 mPa·s.

[0027] In the above technical solution, the viscosity of the organic slurry is 100~500 mPa·s.

[0028] The above-mentioned method for preparing composite dot-coated film includes: coating a composite dot-coating slurry onto a base film by dot coating, drying, and obtaining a coating layer on the base film to obtain a composite dot-coated film.

[0029] In the above technical solution, the base film is made of at least one of polyethylene, polypropylene, polyethylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, polyimide, polyetherimide, polysulfone, polyethersulfone, polyamide, polyphenylene ether, and polyphenylene sulfide.

[0030] In the above technical solution, the thickness of the base film is 2~20μm.

[0031] In the above technical solution, the thickness of the coating on one side (each side) is 0.5~10μm, preferably 4~7μm.

[0032] The above-mentioned composite dot coating film is used to improve the safety and electrochemical performance of lithium batteries.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The composite dot-coating slurry and the matrix arrangement of the coating dots synergistically reduce the risk of particulate matter clogging, improve the air permeability of the separator, and reduce the internal resistance of the lithium battery;

[0035] 2. The ceramic powder (inorganic material) reduces the crystallinity of the organic polymer, and the two work synergistically to improve the interfacial compatibility between the diaphragm and the electrode, thereby increasing the wettability of the diaphragm;

[0036] 3. The ceramic powder in the coating has a strong supporting effect, preventing insufficient cell thickness after hot pressing deformation of the battery, avoiding the risk of reduced cell thickness after hot pressing, and the ceramic powder has high heat resistance, which improves thermal shrinkage and increases the safety performance of the cell.

[0037] 4. The organic polymer in the coating has a good bonding effect. Compared with a single ceramic slurry, the composite dot-coating slurry increases the bonding effect between the electrode and the separator, preventing the electrode from falling off during battery assembly.

[0038] 5. This invention uses a dot-coating method to apply the composite dot-coating slurry instead of full-coverage coating, forming a matrix dot-shaped coating, which reduces the weight of the diaphragm, the amount of coating and the production cost, and has a wider range of applications. Attached Figure Description

[0039] Figure 1 SEM image (magnification 100X) of the composite dot-coated film prepared in Example 10.

[0040] Figure 2 SEM image of the composite dot-coated film prepared in Example 10 (magnification 15kX).

[0041] Figure 3 This is a macroscopic image of the electrode sheet of the lithium battery prepared in Example 19 after disassembly.

[0042] Figure 4 This is a microscope image of the composite dot-coated film prepared in Example 10. Detailed Implementation

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0044] The water used in the following examples is deionized water.

[0045] The electrolyte used in this invention includes an electrolyte and a solvent. The solvent is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EM), with the ratio of EC, DMC, and EM being 1:1:1 by mass. The electrolyte is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L.

[0046] The diaphragm is immersed in the electrolyte, and the liquid absorption rate is calculated according to L=(W1-W2) / W2*100%, where L is the liquid absorption rate, W1 is the weight of the diaphragm after it has reached equilibrium in the electrolyte (no longer absorbs electrolyte), and W2 is the weight of the diaphragm before it is immersed in the electrolyte.

[0047] The diaphragm was heat-treated at 130℃ for 1 hour, and its heat shrinkage rate was calculated. The formula for calculating the heat shrinkage rate is Q=(M1-M2) / M1*100%, where Q is the heat shrinkage rate, M1 is the length or width of the diaphragm before heat treatment, and M2 is the length or width of the diaphragm after heat treatment at 130℃ for 1 hour. When M1 is the length of the diaphragm before heat treatment and M2 is the length of the diaphragm after heat treatment at 130℃ for 1 hour, the longitudinal (MD) heat shrinkage rate is obtained; when M1 is the width of the diaphragm before heat treatment and M2 is the width of the diaphragm after heat treatment at 130℃ for 1 hour, the transverse (TD) heat shrinkage rate is obtained.

[0048] The bonding strength between the diaphragm and the positive electrode sheet: The diaphragm is cut to a size of 25*150mm and the positive electrode sheet to a size of 25*60mm. The temperature of the hot press is adjusted to 80℃ and the pressure to 1000KG. The diaphragm and the positive electrode sheet are preheated for 1 second and hot-pressed for 1 second. After hot pressing, the diaphragm and the positive electrode sheet are tested using an electronic tensile testing machine: The diaphragm and the positive electrode sheet are peeled until the tensile distance of the electronic tensile testing machine is 30mm. The speed of the electronic tensile testing machine is 300mm / min and the peel angle is 180°. The bonding strength between the diaphragm and the positive electrode sheet = peel force divided by the tensile distance of the electronic tensile testing machine. The peel force is the average value of the force collected by the electronic tensile testing machine during the peeling process of the diaphragm and the positive electrode sheet. The bonding strength between the diaphragm and the positive electrode sheet is calculated based on the data of the tensile distance between 10-40mm, that is, the bonding strength between the diaphragm and the positive electrode sheet = peel force between 10-40mm and 30mm. The positive electrode material in the positive electrode sheet is lithium iron phosphate.

[0049] The bonding strength between the diaphragm and the negative electrode sheet is tested in the same way as the bonding strength between the diaphragm and the positive electrode sheet. The only difference is that the "positive electrode sheet" is replaced with the "negative electrode sheet", and the negative electrode material in the negative electrode sheet is graphite.

[0050] Short circuit pass rate (%): Tested according to the national standard GB / T18287-2013. The judgment criteria are that it does not ignite, does not explode, and the external surface temperature is below 150℃.

[0051] 10V / 3C overcharge pass rate (%): Tested according to the national standard GB / T18287-2013. In this invention, the overcharge voltage is set to 10V and the charging current is 3C. The judgment criterion is that it simultaneously meets the requirements of not igniting and not exploding.

[0052] 200-cycle performance: At room temperature, the battery was tested using the Xinwei CT-4000 cell testing equipment. The charge and discharge cycles were performed at a 1C rate, with a charge and discharge voltage range of 3~4.2V. Specifically, the battery was first charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V to a current of 20mA, and then discharged at a constant current of 1C to a voltage of 3.0V. This process was repeated 200 times. The remaining capacity was obtained by dividing the specific capacity of the 200th discharge by the specific capacity of the 1st discharge.

[0053] Internal resistance: Tested according to the method in national standard GB / T18287-2013.

[0054] Examples 1-9

[0055] A method for preparing a composite dot coating slurry includes: mixing a ceramic slurry and an organic slurry, and stirring at room temperature at a revolution speed of 40 r / min and a rotation speed of 1500 r / min for 30 min until homogeneous, to obtain a composite dot coating slurry. The ceramic slurry comprises ceramic material and a first water, with a solid content of 32 wt%. The organic slurry comprises organic material and a second water, with a solid content of 17 wt%. The ratio of ceramic material in the ceramic slurry to organic material in the organic slurry by mass is X, and the value of X is shown in Table 1.

[0056] The method for preparing ceramic slurry includes: mixing first water and first dispersant at room temperature, stirring for 10 minutes until homogeneous, then adding ceramic powder, stirring for 1 hour until homogeneous, and finally adding wetting agent, first thickener and first binder, stirring for 10 minutes until homogeneous to obtain ceramic slurry. The ratio of first dispersant, ceramic powder, wetting agent, first thickener and first binder by mass is 0.6:32:5:7:4. The first thickener is sodium carboxymethyl cellulose (light yellow powder, viscosity 523 cP, 2wt% soluble in water at 25℃), the first binder is polyacrylate emulsion, purchased from Suzhou Derby Electronic Materials Technology Co., Ltd., model DS-985; the first dispersant is an acrylate polymeric dispersant (purchased from Dongguan Aoda Environmental New Materials Co., Ltd., model AD8085); and the wetting agent is an organosilicon nonionic surfactant (polyether-modified dimethyl polysiloxane, purchased from BYK, model LPX). 20900), the ceramic powder is borosilicate (powdered), the particle size of the ceramic powder is D50: 0.35μm, D90: 0.68μm, D99: 1.23μm, the viscosity of the ceramic slurry is 65mpa•s, the rotation speed of the stirring in the method of preparing the ceramic slurry is 2000r / min, and the revolution speed of the stirring is 40r / min;

[0057] The method for preparing the organic slurry includes: mixing the second water and the second dispersant at room temperature, stirring for 10 minutes until homogeneous, then adding the organic polymer, stirring for 1 hour until homogeneous, and finally adding the second thickener and the second binder, stirring for 10 minutes until homogeneous to obtain the organic slurry. The ratio of the second dispersant, organic polymer, second thickener, and second binder by mass is 0.2:18:10:9. The second thickener is sodium carboxymethyl cellulose (light yellow powder, viscosity 523 cP, 2 wt% soluble in water at 25℃), the second binder is polyacrylic acid emulsion, purchased from Sichuan Indile Materials Technology Group Co., Ltd., model LA133; the organic polymer is polyvinylidene fluoride (PVDF, powder, melting point 151-156℃, molecular weight approximately 500,000), and the second dispersant is a cationic ammonium salt dispersant (purchased from BYK, model LP C 22136). The viscosity of the organic slurry is 401 mPa•s. In the method for preparing the organic slurry, the rotation speed of the stirring is 1500 r / min and the revolution speed is 40 r / min.

[0058] Table 1

[0059]

[0060] Comparative Example 1

[0061] A ceramic dotting slurry, specifically the "ceramic slurry" prepared in Example 1.

[0062] Comparative Example 2

[0063] An organic dot coating slurry, specifically the "organic slurry" prepared in Example 1.

[0064] Comparative Example 3

[0065] A method for preparing a composite dot coating slurry includes: mixing water, a first dispersant, ceramic powder, a wetting agent, a first thickener, a first binder, a second dispersant, an organic polymer, a second thickener, and a second binder until homogeneous to obtain a composite dot coating slurry. The ratio of water, the first dispersant, the ceramic powder, the wetting agent, the first thickener, the first binder, the second dispersant, the organic polymer, the second thickener, and the second binder, by mass parts, is 330.3:0.864:46.08:7.2:10.08:5.76:0.2:18:10:9. The first dispersant, the ceramic powder, the wetting agent, the first thickener, the first binder, the second dispersant, the organic polymer, the second thickener, and the second binder are the same as the corresponding substances in Example 1.

[0066] Examples 10-18 and Comparative Examples 4-6

[0067] A method for preparing a dot-coated film includes: applying a slurry to one side of a base film using a dot-coating machine, and then drying it in an oven at 50°C for 1 minute to form a coating on the base film, thereby obtaining a dot-coated film. Figure 4 As shown, the coating dots on the dot-coated film are arranged in a square matrix, with a diameter of approximately 260 μm and a side length of approximately 400 μm. The base film is made of polyethylene (i.e., the base film is a PE film), with a thickness of 12 μm. The coating thickness is Y μm (Y value is shown in Table 2). The slurry is one of the composite dot-coating slurries prepared in Examples 1-9, the ceramic dot-coating slurry prepared in Comparative Example 1, the organic dot-coating slurry prepared in Comparative Example 2, and the composite dot-coating slurry prepared in Comparative Example 3 (the dot-coated film prepared using the composite dot-coating slurry is a composite dot-coated film).

[0068] Table 2

[0069]

[0070] SEM image of the dot-coated film (composite dot-coated film) prepared in Example 10 is shown below. Figure 1 and Figure 2 As shown.

[0071] Comparative Example 7

[0072] A method for preparing a roll-coated film includes: coating a composite dot-coating slurry prepared in Example 1 onto one side of a base film using a microgravure roller, and then drying it in an oven at 60°C for 1 minute to form a coating on the base film, thereby obtaining a roll-coated film. The base film is made of polyethylene (i.e., the base film is a PE film), the thickness of the base film is 12 μm, the coating thickness is 5.4 μm, the microgravure roller has a line count of 80 LPI, and the line depth is 130 μm.

[0073] The basic performance tests of the composite dot-coated films prepared in Examples 10-18, the dot-coated films prepared in Comparative Examples 4-5, the composite dot-coated films prepared in Comparative Example 6, and the roll-coated films prepared in Comparative Example 7 are shown in Table 3.

[0074] Table 3

[0075]

[0076] Table 3 shows that in Examples 10-18, the bonding strength between the separator and the positive electrode sheet, and the bonding strength between the separator and the negative electrode sheet, gradually increased with the increase of PVDF. The composite dot-coated film prepared in Comparative Example 4 showed the lowest bonding strength between the separator and the positive electrode sheet, and the lowest bonding strength between the separator and the negative electrode sheet, indicating that the composite dot-coating slurry has better adhesion than the ceramic dot-coating slurry. In terms of thermal shrinkage, the composite dot-coated film obtained using the composite dot-coating slurry showed significantly improved heat resistance compared to the dot-coated film obtained using pure PVDF slurry (the organic dot-coating slurry in Comparative Example 2), indicating that the composite dot-coated film of this invention has better high-temperature safety performance. From the liquid absorption rate, it can be seen that the composite dot-coated film of this invention has better liquid absorption performance, which is beneficial for high-rate charging and discharging of the battery. The composite dot-coated films prepared in Examples 10-18 have lower contact angles and better wettability. In summary, the composite dot-coated film prepared in Example 18 has the best overall performance.

[0077] Examples 19-27 and Comparative Examples 8-11

[0078] A lithium battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode material in the positive electrode is lithium iron phosphate, the negative electrode material in the negative electrode is graphite, and the separator is one of the composite dot-coated films prepared in Examples 10-18, Comparative Example 6, the dot-coated films prepared in Comparative Examples 4-5, and the roll-coated films prepared in Comparative Example 7. The lithium batteries of Examples 19-27 are obtained sequentially from Examples 10-18, and the lithium batteries of Comparative Examples 8-11 are obtained sequentially from Comparative Examples 4-7.

[0079] Table 4

[0080]

[0081] The lithium battery prepared in Example 19 was disassembled (without cycle testing), and macroscopic images of the electrodes are shown below. Figure 3As shown, the coating points are arranged in a uniform matrix, exhibiting high consistency.

[0082] The lithium battery prepared in Example 19, after 200 cycles at a rate of 0.5C, had a discharge specific capacity of 730 mAh / g and a capacity retention rate of 98%.

[0083] The safety performance test results of the lithium batteries prepared in Examples 19, 23, 27 and Comparative Examples 8-11 are shown in Table 5.

[0084] Table 5

[0085]

[0086] Table 5 shows that the lithium batteries prepared using composite dot-coated films exhibit superior safety performance compared to those prepared using single-slurry dot-coated films (comparative Examples 4 and 5). This is because the synergistic effect of ceramics and organic polymers in the composite dot-coated slurry of this invention endows the lithium batteries with excellent safety performance. In the event of thermal runaway or accidents caused by improper use, it can more effectively prevent lithium battery explosions and other incidents.

[0087] The electrochemical performance test results of the lithium batteries prepared in Examples 19 and Comparative Examples 8-11 are shown in Table 6.

[0088] Table 6

[0089]

[0090] The lithium battery prepared in Comparative Example 11 used a roller-coated film, which covered too much area. When immersed in electrolyte for a long time, the internal resistance increased due to the swelling effect of the polymer, resulting in poor electrolyte retention and failure to perform its electrochemical performance.

[0091] In summary, the coating formed by dot coating can achieve a coating area smaller than the blank area, greatly reducing the weight of the separator and lowering costs. The composite dot coating slurry used in the coating process includes small-particle inorganic materials (ceramic powder) and organic polymers. The small-particle inorganic materials provide strong support, improve the separator interface, and facilitate electrolyte wetting, while also providing heat resistance. Secondly, the use of organic polymers increases the adhesion between the separator and the electrode, resulting in the assembled lithium battery exhibiting good cycle performance.

[0092] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A composite dot-coated film, characterized in that, include: A base film and a coating on the base film, wherein the coating is obtained by coating with a composite dot coating slurry, and the method for preparing the composite dot coating slurry includes: mixing a ceramic slurry and an organic slurry until uniform to obtain a composite dot coating slurry, wherein the ceramic slurry includes: ceramic material and a first water, and the organic slurry includes: organic material and a second water, wherein, by mass parts, the ratio of ceramic material in the ceramic slurry to organic material in the organic slurry is (0.1~20):1; The ceramic material includes: a first dispersant, ceramic powder, a wetting agent, a first thickener, and a first binder; the organic material includes: a second dispersant, an organic polymer, a second thickener, and a second binder.

2. The composite dot-coated film according to claim 1, characterized in that, The solid content of the ceramic slurry is 25-36 wt%, and the solid content of the organic slurry is 15-20 wt%.

3. The composite dot-coated film according to claim 1, characterized in that, In the ceramic material, the ratio of the first dispersant, ceramic powder, wetting agent, first thickener and first binder by mass parts is (0.4~0.8):(28~36):(2~8):(5~9):(1~5).

4. The composite dot-coated film according to claim 1, characterized in that, In the organic material, the ratio of the second dispersant, the organic polymer, the second thickener and the second binder by mass parts is (0.1~0.5):(17~20):(8~12):(7~11).

5. The composite dot-coated film according to claim 1, characterized in that, The organic polymer is one or a mixture of several of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, tetrafluoroethylene-vinylidene fluoride copolymer, and polymethyl methacrylate.

6. The composite dot-coated film according to claim 1, characterized in that, The ceramic powder is one or a mixture of several of the following: alumina, boehmite, silicon dioxide, titanium dioxide, calcium oxide, calcium carbonate, calcium titanate, and barium titanate.

7. The composite dot-coated film according to claim 1, characterized in that, The viscosity of the ceramic slurry is 35~95 mPa·s.

8. The composite dot-coated film according to claim 1, characterized in that, The viscosity of the organic slurry is 100~500 mPa·s.

9. The method for preparing the composite dot-coated film according to any one of claims 1 to 8, characterized in that, include: The composite dot coating slurry is applied to the base film by dot coating and dried to obtain a coating layer on the base film, thus obtaining a composite dot coating film.

10. The application of the composite dot coating film as described in claim 1 in improving the safety and electrochemical performance of lithium batteries.

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