CN113839146B - Lithium-ion battery separator coated with negative electrode active material and its preparation method and application - Google Patents

Abstract

The invention relates to a lithium ion battery diaphragm coated with a negative electrode active material, and belongs to the technical field of diaphragms. The lithium ion battery diaphragm coated with the negative electrode active material comprises a first layer film and a second layer film; the first layer film is a base film, the second layer film comprises a polymer base material, a negative electrode active substance and a conductive agent, and the weight ratio of the polymer base material to the negative electrode active substance to the conductive agent is 0.5-99.5:0.5-99:0.5-10; the negative electrode active material is at least one of a mixture of ceramic particles and graphite, lithium titanate and a silicon-carbon material. The second layer film brings extra battery capacity, and improves the energy density of the battery; the second layer film can play a role of a traditional diaphragm ceramic layer, and can provide the effects of thermal stability and mechanical strength similar to those of traditional ceramic coatings such as alumina; the second film also increases the interfacial stability and compatibility between the separator and the negative electrode.

Description

Lithium-ion battery separator coated with negative electrode active material and its preparation method and application

technical field

The invention relates to a lithium-ion battery diaphragm coated with a negative electrode active material, and belongs to the technical field of diaphragms.

Background technique

With the continuous development of new energy electric vehicles and portable electronic devices, lithium-ion batteries have become the first choice for commercial batteries. In the structure of lithium batteries, the separator is one of the key inner components. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety performance of the battery. A separator with excellent performance plays an important role in improving the overall performance of the battery. The main function of the separator is to separate the positive and negative poles of the battery to prevent the two poles from contacting and short-circuiting. In addition, it also has the function of allowing ions to pass through. The separator material is non-conductive, and its physical and chemical properties have a great influence on the performance of the battery. Since the electrolyte of lithium-ion batteries is an organic solvent system, a diaphragm material resistant to organic solvents is required, and the diaphragm is required to have the following properties:

In the battery system, its chemical stability is better, and the materials used are resistant to organic solvents; the mechanical strength is high, and the service life is long; the ionic conductivity of the organic electrolyte is lower than that of the aqueous solution. In order to reduce the resistance, the electrode area must be as large as possible. Therefore, the diaphragm It must be very thin; when an abnormality occurs in the battery system, the temperature rises. In order to prevent danger, when the rapid heat generation temperature (120-140°C) begins, the thermoplastic separator melts, the micropores are closed, and it becomes an insulator; from lithium batteries From the point of view, it must be fully impregnated by the organic electrolyte, and can maintain a high degree of impregnation during repeated charge and discharge.

Lithium-ion batteries generally use high-strength, thin-film polyolefin-based porous membranes. Commonly used separators include polypropylene (PP) and polyethylene (PE) microporous separators, as well as copolymers of propylene and ethylene, polyethylene homopolymers, etc. . The advantages of applying ceramic powder for diaphragm coating: it can prevent the penetration of lithium dendrites, resist high temperature shrinkage, and ensure the safety of lithium batteries; isolate the positive and negative electrodes to achieve electronic insulation between the positive and negative electrodes; provide ion channels between the positive and negative electrodes , to realize the charging and discharging function of the lithium-ion battery; to absorb and maintain the electrolyte to ensure the cycle life of the lithium battery; to ensure sufficient porosity to ensure the rate characteristics of the lithium-ion battery. Effectively improve the safety indicators of lithium batteries.

At present, the wet-process diaphragm coating materials are dominated by alumina coatings, which occupy the mainstream market share. At the same time, there are PVDF coatings, PVDF/alumina mixed coatings, alumina + PVDF superimposed composite coatings, boehmite, Rich coating categories such as aramid fiber and nanocomposite materials. Because aluminum oxide, as an inorganic substance, has high thermal stability and chemical inertness, it is a good choice for battery separator ceramic coatings. A noteworthy trend is that due to the low hardness of boehmite, there is less wear on machinery during cutting and coating, and the preparation is simpler, which can effectively reduce costs. Compared to alumina, the boehmite coating process consumes less energy and is more environmentally friendly. As a result, boehmite began to occupy the market. However, some studies have also found that the use of boehmite in lithium battery separators will lead to excessive sodium impurities leaching into the electrolyte, which will lead to thermal runaway, low efficiency and shortened life of lithium batteries. In addition, although the inert coating based on alumina and boehmite can improve the stability of the separator, it reduces the energy density of the battery.

Contents of the invention

The technical problem to be solved by the present invention is to provide a lithium-ion battery separator coated with negative electrode active material.

In order to solve the above-mentioned first technical problem, the negative electrode active material coated lithium ion battery diaphragm of the present invention includes a first layer of film and a second layer of film; the first layer of film is a base film, and the second layer of film includes a polymeric Material substrate, negative electrode active material, conductive agent, the weight ratio of described polymer substrate, negative electrode active material, conductive agent is 0.5～99.5:0.5～99:0.5～10; Preferably described polymer substrate, negative electrode active The weight ratio of the substance and the conductive agent is 0.5-99.5:0.5-95:2.5-5;

The negative electrode active material is at least one of a mixture of ceramic particles and graphite, lithium titanate, and silicon-carbon materials.

In a specific embodiment, the base film is polypropylene, polyethylene, double-layer polypropylene/polyethylene composite film, three-layer polypropylene/polyethylene/polypropylene composite film, nitrocellulose membrane, cellulose acetate Film, polyamide film, polyethylene terephthalate, polyester film, thermoplastic polyimide, thermosetting polyimide, polyamide-imide, polyetherimide, abrasive fiber film, poly Phthamide membrane, metal membrane, alloy membrane, ceramic membrane, molecular sieve composite membrane, zeolite membrane or glass membrane.

In a specific embodiment, the polymer substrate is polyvinylidene fluoride-based polymer, polybutyl acrylate, polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, Polyvinylidene fluoride, polybismethoxyethoxyethoxyethanol salt-phosphazene, polyvinyl chloride, polydimethylsiloxane, polyvinylidene fluoride-hexafluoropropylene, polyperfluorosulfonic acid, sulfonated Polytetrafluoroethylene, sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene, sulfonated polyaluminum, sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated polystyrene, sulfonated polyimide ﹑sulfonated styrene-butadiene copolymer ﹑sulfonated polychlorotrifluoroethylene, sulfonated perfluoroethylene-propylene copolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer ﹑sulfonated polyvinylidene fluoride, At least one of polyvinylidene fluoride, sulfonated copolymer of hexafluoropropylene and tetrafluoroethylene, sulfonated copolymer of ethylene and tetrafluoroethylene, polybenzimidazole, and its chemical derivatives and copolymers.

In a specific embodiment, the conductive agent is one or more of acetylene black, 350G, carbon fiber, carbon nanotube, Ketjen Black, graphite conductive agent, graphene, Super P; the Ketjen Black Preferably KetjenblackEC300J, KetjenblackEC600JD, Carbon ECP, Carbon ECP600JD; the graphite conductive agent is preferably KS-6, KS-15, SFG-6, SFG-15.

In a specific implementation manner, the thickness of the first layer of film is 5-40 μm, and the thickness of the second layer of film is 1-20 μm.

The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned negative electrode active material-coated lithium-ion battery separator.

In order to solve the second technical problem of the present invention, the preparation method of the lithium-ion battery diaphragm coated with the negative electrode active material comprises:

a. Add the polymer substrate to the solvent, and stir to form a stable slurry A;

b. adding conductive agent to the slurry and stirring evenly to form slurry B;

c. adding the negative electrode active material to the above-mentioned slurry B and dispersing it uniformly to obtain slurry C;

d. Apply the slurry C evenly on the base film and remove the solvent;

Preferably, the mass of the solvent accounts for 60-80% of the total mass of the slurry C;

The steps a~c are preferably carried out in a closed container.

In a specific embodiment, the homogeneous dispersion in step c is to stir evenly and perform ultrasonic dispersion, and continue to stir after ultrasonic; the stirring is preferably 500-1000r/min, stirring for 12-24h; the ultrasonic is preferably 30- 40kHz, last 25~35min;

In step d, the slurry C is evenly coated on the base film by spraying, casting, screen printing, dipping or electrophoresis.

In a specific embodiment, the solvent is selected from: N-methylpyrrolidone, acetone, 1,3-dioxolane, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, Poly(ethylene glycol) dimethyl ether, diethylene glycol dibutyl ether, 2-ethoxyethyl ether, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl formate, benzene, toluene, Xylene, methyl acetate, fluoroethylene carbonate, vinylene carbonate, allyl ethyl carbonate, hydrofluoroether, ionic liquid solvent, cyclohexane, cyclohexanone, toluene cyclohexanone, chlorobenzene, Dichlorobenzene, dichloromethane, isopropanol, ethyl ether, propylene oxide, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl butanone, methyl isobutyl ketone diethyl ester, ethyl propionate , methyl propionate, propylene carbonate, γ-butyrolactone, acetonitrile, ethyl acetate, propyl formate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetonitrile, pyridine, at least one of phenols.

The third technical problem to be solved by the present invention is to provide the application of the lithium-ion battery diaphragm coated with the above-mentioned negative electrode active material in the preparation of lithium-ion batteries, the positive electrode of the battery faces the second layer of film, and the negative electrode faces the first layer membrane.

In a specific embodiment, the material of the positive electrode of the battery contains the negative electrode active material.

The negative electrode active material contained in the positive electrode material of the battery means that the negative electrode active material is the same as the positive electrode material, and the effect is better. For example, the positive electrode is lithium titanate, so the negative electrode active material is lithium titanate. Under the premise of not reducing the safety, the active material in the separator can contribute energy to the battery, and a battery separator with better performance can be obtained.

Beneficial effect:

The second film of the present invention brings additional battery capacity and improves the energy density of the battery;

The second film of the present invention can function as a traditional separator ceramic layer, and can provide thermal stability and mechanical strength effects similar to traditional ceramic coatings such as alumina;

In addition, the second film also increases the interface stability and compatibility between the separator and the negative electrode.

Description of drawings

Figure 1 is the contact angle test;

Fig. 2 is the tension test of the membrane that embodiment prepares;

Fig. 3 is comparative examples 1 and 2, embodiment 2 and the cycle test experiment in which PP is directly used as a diaphragm.

Fig. 4 is a cycle test experiment of comparative examples 1 and 2, embodiment 1 and using PP as a diaphragm directly.

Detailed ways

In order to solve the above-mentioned first technical problem, the negative electrode active material coated lithium ion battery diaphragm of the present invention includes a first layer of film and a second layer of film; the first layer of film is a base film, and the second layer of film includes a polymeric Material substrate, negative electrode active material, conductive agent, the weight ratio of described polymer substrate, negative electrode active material, conductive agent is 0.5～99.5:0.5～99:0.5～10; Preferably described polymer substrate, negative electrode active The weight ratio of the substance and the conductive agent is 0.5-99.5:0.5-95:2.5-5;

The negative electrode active material is at least one of a mixture of ceramic particles and graphite, lithium titanate, and silicon-carbon materials.

In a specific embodiment, the base film is polypropylene, polyethylene, double-layer polypropylene/polyethylene composite film, three-layer polypropylene/polyethylene/polypropylene composite film, nitrocellulose membrane, cellulose acetate Film, polyamide film, polyethylene terephthalate, polyester film, thermoplastic polyimide, thermosetting polyimide, polyamide-imide, polyetherimide, abrasive fiber film, poly Phthamide membrane, metal membrane, alloy membrane, ceramic membrane, molecular sieve composite membrane, zeolite membrane or glass membrane.

In a specific embodiment, the polymer substrate is polyvinylidene fluoride-based polymer, polybutyl acrylate, polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, Polyvinylidene fluoride, polybismethoxyethoxyethoxyethanol salt-phosphazene, polyvinyl chloride, polydimethylsiloxane, polyvinylidene fluoride-hexafluoropropylene, polyperfluorosulfonic acid, sulfonated Polytetrafluoroethylene, sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene, sulfonated polyaluminum, sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated polystyrene, sulfonated polyimide ﹑sulfonated styrene-butadiene copolymer ﹑sulfonated polychlorotrifluoroethylene, sulfonated perfluoroethylene-propylene copolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer ﹑sulfonated polyvinylidene fluoride, At least one of polyvinylidene fluoride, sulfonated copolymer of hexafluoropropylene and tetrafluoroethylene, sulfonated copolymer of ethylene and tetrafluoroethylene, polybenzimidazole, and its chemical derivatives and copolymers.

In a specific embodiment, the conductive agent is one or more of acetylene black, 350G, carbon fiber, carbon nanotube, Ketjen Black, graphite conductive agent, graphene, Super P; the Ketjen Black Preferably KetjenblackEC300J, KetjenblackEC600JD, Carbon ECP, Carbon ECP600JD; the graphite conductive agent is preferably KS-6, KS-15, SFG-6, SFG-15.

In a specific implementation manner, the thickness of the first layer of film is 5-40 μm, and the thickness of the second layer of film is 1-20 μm.

The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned negative electrode active material-coated lithium-ion battery separator.

In order to solve the second technical problem of the present invention, the preparation method of the lithium-ion battery diaphragm coated with the negative electrode active material comprises:

a. Add the polymer substrate to the solvent, and stir to form a stable slurry A;

b. adding conductive agent to the slurry and stirring evenly to form slurry B;

c. adding the negative electrode active material to the above-mentioned slurry B and dispersing it uniformly to obtain slurry C;

d. Apply the slurry C evenly on the base film and remove the solvent;

Preferably, the mass of the solvent accounts for 60-80% of the total mass of the slurry C;

The steps a~c are preferably carried out in a closed container.

In a specific embodiment, the homogeneous dispersion in step c is to stir evenly and perform ultrasonic dispersion, and continue to stir after ultrasonic; the stirring is preferably 500-1000r/min, stirring for 12-24h; the ultrasonic is preferably 30- 40kHz, last 25~35min;

In step d, the slurry C is evenly coated on the base film by spraying, casting, screen printing, dipping or electrophoresis.

In a specific embodiment, the solvent is selected from: N-methylpyrrolidone, acetone, 1,3-dioxolane, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, Poly(ethylene glycol) dimethyl ether, diethylene glycol dibutyl ether, 2-ethoxyethyl ether, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl formate, benzene, toluene, Xylene, methyl acetate, fluoroethylene carbonate, vinylene carbonate, allyl ethyl carbonate, hydrofluoroether, ionic liquid solvent, cyclohexane, cyclohexanone, toluene cyclohexanone, chlorobenzene, Dichlorobenzene, dichloromethane, isopropanol, ethyl ether, propylene oxide, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl butanone, methyl isobutyl ketone diethyl ester, ethyl propionate , methyl propionate, propylene carbonate, γ-butyrolactone, acetonitrile, ethyl acetate, propyl formate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetonitrile, pyridine, at least one of phenols.

The third technical problem to be solved by the present invention is to provide the application of the lithium-ion battery diaphragm coated with the above-mentioned negative electrode active material in the preparation of lithium-ion batteries, the positive electrode of the battery faces the second layer of film, and the negative electrode faces the first layer membrane.

In a specific embodiment, the material of the positive electrode of the battery contains the negative electrode active material.

The negative electrode active material contained in the positive electrode material of the battery means that the negative electrode active material is the same as the positive electrode material, and the effect is better. For example, the positive electrode is lithium titanate, so the negative electrode active material is lithium titanate. Under the premise of not reducing the safety, the active material in the separator can contribute energy to the battery, and a battery separator with better performance can be obtained.

The specific implementation of the present invention will be further described below in conjunction with the examples, and the present invention is not limited to the scope of the examples.

Example 1

The first layer of separator is PP base film.

Preparation steps of the second layer of diaphragm solution:

(1), take by weighing 0.14g polymer substrate polyvinylidene fluoride (PVDF), Ketjen black KetjenblackEC300J0.06g, negative electrode active material is the mixture 1.8g of silicon powder and graphite, wherein the mass ratio of silicon powder and graphite is 1:89, and measure the solvent N-methylpyrrolidone (NMP), accounting for 80% of the total mass of the solution.

(2) Add the polymer substrate PVDF into the solvent, and stir to form a stable transparent colloid;

(3) Add 0.06 g of conductive agent Ketjen Black to the above-mentioned colloid to form a second colloid.

(4) Add the negative electrode active material graphite containing 1% silicon powder into the second colloid, stir evenly and perform ultrasonic dispersion for 30 minutes. Steps (2) to (4) are carried out in an airtight container.

(5) Continue to stir the ultrasonicated glue solution for 18 hours, mix evenly, and form a slurry for the second layer of diaphragm.

(6) Using the slurry prepared in the above method, cast the second part of the colloid on the PP commercial base film to ensure that the thickness of the second film is between 1 and 20 μm.

(7) Put the electrode slurry coated in step (6) with a uniform thickness in a vacuum oven at 60 degrees Celsius for 18 hours, and the vacuum degree is the lowest.

(8) Store the diaphragm package dried in (7), take two pieces and a smooth and clean plastic film, and sandwich the diaphragm between them.

The graphite/metal lithium button half-battery is used for testing, and the battery graphite pole piece (positive electrode) is composed of 90% graphite, 7% polymer, and 3% conductive agent. The electrolyte is a secondary electrolyte LB-063 with a formula of 1.0M LiPF6 in EC:DMC=3:7Vol%. When the battery is assembled, the lithium titanate electrode faces the second layer of film, and the lithium metal sheet faces the first layer of film. After the battery is installed, the battery cycle test is carried out on the Xinwei battery test system under the condition of 25 degrees Celsius. The weight of the active material contained in a single pole piece is calculated by the total weight of the lithium titanate electrode, and then the weight of the active material contained in a single electrode is calculated by i _1C = M activity *Theoretical capacity/1000, calculate the size of the 0.1C and 0.5C currents that are cycled during the battery test, and for the cycle test, it is necessary to perform a 0.1C charge and discharge test on the battery for 2-3 laps. This test is mainly It is to activate the battery so that the battery capacity can be optimized. In the follow-up, the battery will be charged and discharged at a rate of 0.5C to observe its cycle performance. The test results of Example 1 and Comparative Example are shown in Table 1 and Figure 4 for details.

Table 1 Cycle performance test results

product Efficiency % for 50 cycles 50 cycle capacity mAh/g Cycle 100 laps efficiency% 100 cycle capacity mAh/g Example 1 101 345 99.8 347 Comparative example 1 101 293.3 100.5 294.5 Comparative example 2 101 289.3 100.5 291.3 PP 99.8 283 99.8 285

Example 2

The difference between this embodiment and embodiment 1 is that the negative electrode active material is lithium titanate, and other steps are the same as in embodiment 1.

Lithium titanate/metal lithium button half-battery is used for testing. The battery lithium titanate pole piece (positive electrode) is composed of 90% lithium titanate, 5% conductive agent, 5% polymer, and the electrolyte is formulated as 1.0M LiPF6 in EC:DMC=3:7Vol% secondary electrolyte LB-063. When the battery is assembled, the lithium titanate electrode faces the second layer of film, and the lithium metal sheet faces the first layer of film. After the battery is installed, the battery cycle test is carried out on the Xinwei battery test system under the condition of 25 degrees Celsius. The weight of the active material contained in a single pole piece is calculated by the total weight of the lithium titanate electrode, and then the weight of the active material contained in a single electrode is calculated by i _1C = M activity *Theoretical capacity/1000, calculate the size of the 0.1C and 0.5C currents that are cycled during the battery test, and for the cycle test, it is necessary to perform a 0.1C charge and discharge test on the battery for 2-3 laps. This test is mainly It is to activate the battery so that the battery capacity can be optimized. In the follow-up, the battery will be charged and discharged at a rate of 0.5C to observe its cycle performance. The test results of Example 1 and Comparative Example are shown in Table 2 and Figure 3.

Table 2 Cycle performance test results

product Efficiency % for 50 cycles 50 cycle capacity mAh/g Cycle 100 laps efficiency% 100 cycle capacity mAh/g Example 2 99.9 165.4 99.7 162.4 Comparative example 1 100.3 144.7 99.6 141.7 Comparative example 2 99 143.8 99.2 140.5 PP 99.9 141.4 99.5 140

Comparative example 1

The difference between this experiment and Example 1 is that the weight of the second film PVDF polymer accounts for 97% of the weight of the film-forming material, superconducting carbon black accounts for 3% of the weight of the film-forming material, and there is no negative electrode active material.

Comparative example 2

The difference between this experiment and Example 1 is that the weight of the second layer of film PVDF polymer accounts for 7% of the weight of the film-forming substance, superconducting carbon black accounts for 3% of the weight of the film-forming substance, aluminum oxide (Al ₂ O ₃ ) The specific gravity is 90%.

It can be seen from the contact angle test in Figure 1 that compared with the PP film, the Si/C film coated in Example 1-2, the lithium titanate (Li ₄ Ti ₅ O ₁₂ ) coating film is more hydrophilic.

The tensile strength and tensile fracture rate of the coated separator in Figure 2 are significantly improved, and the mechanical properties are increased.

It can be seen from Figure 3 and Figure 4 that the battery capacity is significantly improved by the separator. For the PP film and the film coated with aluminum oxide and 97% PVDF, the difference in battery capacity is not large, but the stability and mechanical properties of the separator are enhanced, but The coating of lithium titanate and Si/C of the present invention can significantly improve the capacity. The increase in the number of cycles shows that the coating layer is more stable.

Claims (11)

1. The separator of lithium ion battery coated with the negative electrode active material is characterized in that, the separator comprises a first layer of film and a second layer of film; the first layer of film is a base film, and the second layer of film comprises a polymer substrate , negative electrode active material, conductive agent, the weight ratio of described polymer substrate, negative electrode active material, conductive agent is 7:90:3, the thickness of described first layer film is 5～40 μ m, the thickness of second layer film 1～20μm; The negative electrode active material is a mixture of silicon powder and graphite, wherein the mass ratio of silicon powder and graphite is 1:89; the polymer substrate is a polyvinylidene fluoride-based polymer; the conductive agent is Ketjenblack KetjenblackEC300J . 2. the negative active material coating lithium-ion battery diaphragm according to claim 1, is characterized in that, described base film is polypropylene, polyethylene, double-layer polypropylene/polyethylene composite film, three-layer polypropylene/ Polyethylene/polypropylene composite film, nitrocellulose film, cellulose acetate film, polyamide film, polyethylene terephthalate, polyester film, thermoplastic polyimide, thermosetting polyimide, polyamide -imide, polyetherimide, abrasive fiber membrane, polyamide membrane, metal membrane, alloy membrane, ceramic membrane, molecular sieve composite membrane, zeolite membrane or glass membrane. 3. the preparation method of the lithium-ion battery diaphragm coated with negative electrode active material as claimed in claim 1 or 2, is characterized in that, described method comprises: a. Add the polymer substrate to the solvent, and stir to form a stable slurry A; b. adding conductive agent to the slurry and stirring evenly to form slurry B; c. adding the negative electrode active material to the above-mentioned slurry B and dispersing it uniformly to obtain slurry C; d. Apply the slurry C evenly on the base film and remove the solvent. 4 . The method for preparing a negative electrode active material-coated lithium-ion battery separator according to claim 3 , wherein the mass of the solvent accounts for 60-80% of the total mass of the slurry C. 5 . 5 . The preparation method of the negative electrode active material-coated lithium ion battery separator according to claim 3 , characterized in that steps a to c are carried out in a closed container. 5 . 6. the preparation method of the lithium-ion battery diaphragm that negative electrode active material coats according to claim 3 is characterized in that, the uniform dispersion described in c step is to stir evenly and carry out ultrasonic dispersion, continue to stir after ultrasonic; In step d, the slurry C is evenly coated on the base film by spraying, casting, screen printing, dipping or electrophoresis. 7 . The method for preparing a negative electrode active material-coated lithium-ion battery separator according to claim 6 , wherein the stirring is 500-1000 r/min for 12-24 hours. 8 . The method for preparing a negative electrode active material-coated lithium-ion battery separator according to claim 6 , wherein the ultrasonic wave is 30-40 kHz and lasts for 25-35 min. 9. according to the preparation method of the lithium-ion battery separator that negative electrode active material is coated with according to claim 3 or 4, it is characterized in that, described solvent is selected from: N-methylpyrrolidone, acetone, 1,3-dioxolane Cyclo, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, poly(ethylene glycol) dimethyl ether, diethylene glycol dibutyl ether, 2-ethoxyethyl ether, ethylene carbonate ester, dimethyl carbonate, ethyl methyl carbonate, methyl formate, benzene, toluene, xylene, methyl acetate, fluoroethylene carbonate, vinylene carbonate, allyl ethyl carbonate, hydrofluoroether , ionic liquid solvent, cyclohexane, cyclohexanone, toluene cyclohexanone, chlorobenzene, dichlorobenzene, dichloromethane, isopropanol, ether, propylene oxide, methyl acetate, ethyl acetate, propyl acetate , acetone, methyl butanone, methyl isobutyl ketone diethyl ester, ethyl propionate, methyl propionate, propylene carbonate, γ-butyrolactone, acetonitrile, ethyl acetate, propyl formate, ethylene glycol At least one of monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetonitrile, pyridine, and phenol. 10. The application of the lithium-ion battery separator coated with negative electrode active material as claimed in claim 1 or 2 in the preparation of lithium-ion battery, the positive electrode of the battery faces the second layer of film, and the negative electrode faces the first layer of film. 11. The application according to claim 10, characterized in that the material of the positive electrode of the battery contains the negative electrode active material.