CN114142028B - Negative electrode material, negative electrode sheet, preparation method and application thereof - Google Patents

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a negative electrode material, a negative electrode sheet, a preparation method and application thereof. The negative electrode material provided by the invention comprises a graphite material, a binder and a conductive agent; the graphite material comprises a first graphite material and a second graphite material; wherein the first graphite material is selected from the group consisting of a particle size D50 of 9-20 μm and a specific surface area of 0.9-2.0m ² Artificial graphite/g; the second graphite material is selected from the group consisting of particles having a D50 of 3-9 μm and a specific surface area of 1.8-3.5m ² /g artificial graphite. The negative electrode material provided by the invention can effectively improve the energy density and the power performance of the lithium ion battery, reduce the battery impedance, and improve the energy density of the power battery on the premise that the high-power performance requirement of the PHEV type automobile can be ensured when the negative electrode material is applied to the PHEV type automobile, thereby improving the driving mileage of the automobile.

Description

Negative electrode material, negative electrode sheet, preparation method and application thereof

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a negative electrode material, a negative electrode sheet and a preparation method and application thereof.

Background technique

As a new type of high-energy green battery, lithium-ion batteries have shown broad application prospects in portable electronic devices, electric vehicles, and defense industries with the characteristics of high voltage, high capacity and long cycle life. Among them, electric vehicles are gradually replacing Fuel vehicles have become an irreversible trend and become a key means to solve the increasingly prominent energy crisis and environmental pollution. However, due to the limitation of the battery chemical system, compared with traditional fuel vehicles, electric vehicles currently on the market still face a battery life. Many problems such as short mileage and poor safety performance have greatly hindered the acceptance of electric vehicles by end consumers. For plug-in hybrid new energy vehicles using hybrid batteries, the energy supply can be provided by batteries and fuel respectively. The car requires high power under the working conditions of start-stop, acceleration and low speed, resulting in high fuel consumption and emissions. This working condition The power battery provides high-power energy, which can reduce fuel consumption and bring a quiet and smooth low-speed congestion experience. Under high-speed conditions, fuel can be used to provide energy, and it can work at a stable low speed for a long time, while supporting a longer cruising range.

Due to its power-demanding design, the traditional PHEV (plug-in hybrid electric vehicle) hybrid battery has a lower capacity and less energy than the traditional pure electric power battery. The further expansion of the application of power batteries, so the development of a PHEV hybrid battery that takes into account both energy and power has become an important means to solve the disadvantages of new energy vehicle development. However, PHEV hybrid batteries are mostly lithium-ion batteries, and the negative electrode material is very important to improve the performance of the battery. The negative electrode material of the existing lithium-ion battery uses graphite material, binder and conductive agent as the negative electrode active material, but the existing negative electrode material cannot effectively balance the energy density and power performance of the battery.

Contents of the invention

In order to overcome the defect that the existing negative electrode materials cannot effectively balance the energy density and power performance of the battery, a negative electrode material, a negative electrode sheet, and a preparation method and application thereof are provided.

To achieve the above object, the present invention adopts the following technical solutions:

A negative electrode material, the negative electrode material includes a graphite material, a binder and a conductive agent; the graphite material includes a first graphite material and a second graphite material; wherein the first graphite material is selected from a particle size D50 of 9-20 μm, Artificial graphite with a specific surface area of 0.9-2.0 m ² /g; the second graphite material is selected from artificial graphite with a particle size D50 of 3-9 μm and a specific surface area of 1.8-3.5 m ² /g.

Preferably, the artificial graphite in the first graphite material is obtained from needle coke, which is calcined and graphitized and then granulated.

Preferably, the calcination temperature is 2800-3200° C., and the calcination time is 18-25 days.

The first graphite material in the present invention is selected from artificial graphite with a particle size D50 of 9-20 μm and a specific surface area of 0.9-2.0 m ² /g. The artificial graphite is obtained by calcining and graphitizing needle coke as a raw material at a high temperature. It is a high-capacity artificial graphite with a gram capacity of 350-360mAh/g at a rate of 0.1C and an initial charge-discharge efficiency of ≥92%. The second graphite material is selected from the artificial graphite whose particle size D50 is 3-9 μm and whose specific surface area is 1.8-3.5 m ² /g. The gram capacity at C rate is 340±5mAh/g, and the first charge and discharge efficiency is ≥90%.

Preferably, based on the total mass of the graphite material, the mass proportion of the first graphite material is 30-95%, and the mass proportion of the second graphite material is 5-70%.

Preferably, based on the total mass of the graphite material, the mass proportion of the first graphite material is 70-90%, and the mass proportion of the second graphite material is 10-30%.

Preferably, the mass proportion of graphite material in the negative electrode material is 70-99.9%, the mass proportion of binder is 0.05-15%, and the mass proportion of conductive agent is 0.05-15%.

Optionally, the mass proportion of the second graphite material in the negative electrode material is 3-20%.

Preferably, the binder is selected from at least one of polyacrylonitrile, carboxymethyl cellulose salt, and water-based binder;

The water-based binder is selected from one or more of polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), sodium alginate (ALG), and fluorinated rubber.

Preferably, the binder is polyacrylonitrile, carboxymethyl cellulose salt and water-based binder;

The mass proportion of polyacrylonitrile in the negative electrode material is 0.5-5.0%, the mass proportion of carboxymethyl cellulose salt is 0.1-3.0%, and the mass proportion of water-based binder is 0.1-3.0%.

Preferably, based on the total mass of the binder, the mass proportion of polyacrylonitrile is 1-90%, the mass proportion of carboxymethyl cellulose salt is 1-50%, and the mass proportion of water-based binder is 9-49%;

Preferably, based on the total mass of the binder, the mass proportion of polyacrylonitrile is 30-70%, the mass proportion of carboxymethyl cellulose salt is 5-30%, and the mass proportion of water-based binder 25-40%.

Preferably, the carboxymethylcellulose salt is sodium carboxymethylcellulose.

Preferably, the conductive agent is selected from one or more of carbon nanotubes, graphene, conductive graphite, conductive carbon black, Ketjen Black ECP, and carbon fiber (VGCF).

The present invention also provides a negative electrode sheet, which includes a current collector and a negative electrode material loaded on the current collector, and the negative electrode material is the above-mentioned negative electrode material.

The present invention also provides a method for preparing the above-mentioned negative electrode sheet. The graphite material, binder, conductive agent and water are mixed to form a slurry, and then the slurry is coated on the surface of the current collector, dried and rolled and die-cutting to obtain the negative electrode sheet.

Preferably, the amount of water added is 3-10% of the total mass of graphite material, binder and conductive agent.

The present invention also provides a lithium ion battery. The lithium ion battery includes a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte, and the negative electrode sheet is the above-mentioned negative electrode sheet or the negative electrode sheet prepared by the above-mentioned preparation method.

The present invention does not specifically limit the composition of the positive electrode sheet, separator and electrolyte. Preferably, the positive electrode sheet includes a current collector and a positive electrode material coated on the surface of the current collector, and the positive electrode material includes an active material, a conductive agent and a binder. The active material is selected from lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminate (NCA), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium-rich manganese base, cobalt acid One or more of sodium (NCO), sodium iron phosphate (NFP), and sodium manganate (NMO), with a particle size of 5-100 μm and a mass proportion of 70-99.9%. The conductive agent is selected from one or more of carbon nanotubes (CNT), graphene, conductive graphite, conductive carbon black, Ketjen black ECP, carbon fiber (VGCF), and the mass ratio of the conductive agent is 0.1-15 %. The binder is selected from one or more of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), fluorinated rubber, and polyurethane. The binder accounts for 0.1-15%.

Preferably, the separator is selected from one or more of a single-layer PE (polyethylene) film, a single-layer PP (polypropylene) film, a three-layer PP/PE/PP composite film, and a non-woven fabric film. It can be understood that the diaphragm of the present invention also includes a film formed by compounding at least two of PE, PP, and non-woven fabrics. It can also be a film formed by coating a functional coating on the above-mentioned film. It can also be a coated film. Ceramic diaphragm coated with alumina layer, rubberized diaphragm coated with PVDF layer, and composite diaphragm coated with ceramic rubberized mixed coating.

Preferably, the electrolyte is composed of organic solvent, lithium salt and additives. The organic solvent is formed by mixing ethylene carbonate (EC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), and its mixing ratio is (10-30) :(5-20):(10-30):(35-50). The lithium salt is lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisoxalate borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium trifluoromethanesulfonate (LiCF3SO3), bis(trifluoromethane One or more of lithium sulfonyl imides (LiN(CF3SO2)2). The additives are ethylene sulfate (DTD), propylene sulfite (PS), propene sultone (RPS), methylene methyl disulfonate (MMDS), vinylene carbonate (VC), butyl One or several components of dinitrile (SN).

The present invention does not specifically limit the preparation process of lithium-ion batteries, which can be prepared by conventional methods in the field. Optionally, the prepared positive electrode, negative electrode, and diaphragm can be made into pole cores by lamination methods and put into aluminum shells. It is prepared after injection, encapsulation and activation.

Beneficial effects of the present invention:

1. The negative electrode material provided by the present invention uses artificial graphite with a particle size D50 of 9-20 μm and a specific surface area of 0.9-2.0 m ² /g as the first graphite material. The artificial graphite uses needle coke as a raw material and undergoes high-temperature calcined graphite The obtained artificial graphite is a high-capacity artificial graphite; the second graphite material is selected from artificial graphite with a particle size D50 of 3-9 μm and a specific surface area of 1.8-3.5m ² /g, and the artificial graphite is a high-power type Artificial graphite has small particles and large specific surface. The present invention adopts specific first graphite material and second graphite material, utilizes the high-capacity characteristics of the first graphite material, and the high-power characteristics of the second graphite material, and the two interact with each other. Cooperate, the obtained negative electrode material can effectively improve the energy density and power performance of lithium-ion batteries, reduce the battery impedance, apply it to PHEV vehicles to ensure the high power performance requirements of PHEV vehicles, and improve the energy density of power batteries , so as to increase the mileage of the car and make the battery take into account both energy type and power type.

2. For the negative electrode material provided by the present invention, further, based on the total mass of the graphite material, the mass proportion of the first graphite material is 30-95%, and the mass proportion of the second graphite material is 5-70%. Further preferably, based on the total mass of the graphite material, the mass proportion of the first graphite material is 70-90%, and the mass proportion of the second graphite material is 10-30%. By controlling the ratio of the first graphite material and the second graphite material, the present invention can further improve the energy density and power performance of the lithium-ion battery while reducing the battery impedance.

3. The negative electrode material provided by the present invention, further, the binder is polyacrylonitrile, carboxymethyl cellulose salt and water-based binder; the present invention can further ensure that the prepared The battery can take into account excellent energy density and power performance, while effectively reducing the battery impedance.

Detailed ways

The following examples are provided in order to further understand the present invention better, are not limited to the best implementation mode, and do not limit the content and protection scope of the present invention, anyone under the inspiration of the present invention or use the present invention Any product identical or similar to the present invention obtained by combining features of other prior art falls within the protection scope of the present invention.

If no specific experimental steps or conditions are indicated in the examples, it can be carried out according to the operation or conditions of the conventional experimental steps described in the literature in this field. The reagents or instruments used, whose manufacturers are not indicated, are all commercially available conventional reagent products.

Example 1

This embodiment provides a kind of negative electrode material, and described negative electrode material comprises graphite material, binding agent, conductive agent, and described graphite material is made of first graphite material (the first graphite material is selected from particle diameter D50 is 12 μm, and specific surface area is 1.2 m ² /g of artificial graphite, the artificial graphite is obtained by calcining needle coke for 21 days at 2800°C for graphitization, and then granulating), the second graphite material (the second graphite material is selected from the particle size D50 is 6 μm, specific surface area is 2.5m ² /g artificial graphite) composition, described binding agent is polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, and described conductive agent is conductive carbon black; The mass proportion of graphite material in the negative electrode material is 95.5%, the mass proportion of conductive agent is 1%, the mass proportion of polyacrylonitrile is 2.5%, the mass proportion of carboxymethyl cellulose sodium is 0.3%, styrene-butadiene The mass proportion of the rubber is 0.7%, wherein based on the total mass of the graphite material, the mass proportion of the first graphite material is 90%, and the mass proportion of the second graphite material is 10%.

This embodiment also provides a negative electrode sheet, and the preparation method of the negative electrode sheet includes the following steps:

Mix the above-mentioned graphite material, binder and conductive agent, then add 3% water of the total mass of graphite material, binder and conductive agent, mix uniformly to prepare a slurry, and then coat the slurry on the negative electrode current collector copper foil The surface is dried, rolled and die-cut to obtain the negative electrode sheet.

Example 2

This embodiment provides a kind of negative electrode material, and described negative electrode material comprises graphite material, binding agent, conductive agent, and described graphite material is made of first graphite material (the first graphite material is selected from particle diameter D50 is 12 μm, and specific surface area is 1.2 m ² /g of artificial graphite, the artificial graphite is obtained by calcining needle coke for 21 days at 2800°C for graphitization, and then granulating), the second graphite material (the second graphite material is selected from the particle size D50 is 6 μm, specific surface area is 2.5m ² /g artificial graphite) composition, described binding agent is polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, and described conductive agent is conductive carbon black; The mass proportion of graphite material in the negative electrode material is 95.5%, the mass proportion of conductive agent is 1%, the mass proportion of polyacrylonitrile is 2.5%, the mass proportion of carboxymethyl cellulose sodium is 0.3%, styrene-butadiene The mass proportion of the rubber is 0.7%, wherein based on the total mass of the graphite material, the mass proportion of the first graphite material is 85%, and the mass proportion of the second graphite material is 15%.

This embodiment also provides a negative electrode sheet, and the preparation method of the negative electrode sheet includes the following steps:

Mix the above-mentioned graphite material, binder and conductive agent, then add 3% water of the total mass of graphite material, binder and conductive agent, mix uniformly to prepare a slurry, and then coat the slurry on the negative electrode current collector copper foil The surface is dried, rolled and die-cut to obtain the negative electrode sheet.

Example 3

This embodiment provides a kind of negative electrode material, and described negative electrode material comprises graphite material, binding agent, conductive agent, and described graphite material is made of first graphite material (the first graphite material is selected from particle diameter D50 is 12 μm, and specific surface area is 1.2 m ² /g of artificial graphite, the artificial graphite is obtained by calcining needle coke for 21 days at 2800°C for graphitization, and then granulating), the second graphite material (the second graphite material is selected from the particle size D50 is 6 μm, specific surface area is 2.5m ² /g artificial graphite) composition, described binding agent is polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, and described conductive agent is conductive carbon black; The mass proportion of graphite material in the negative electrode material is 95%, the mass proportion of conductive agent is 1.5%, the mass proportion of polyacrylonitrile is 2.5%, the mass proportion of carboxymethyl cellulose sodium is 0.3%, styrene-butadiene The mass proportion of the rubber is 0.7%, wherein based on the total mass of the graphite material, the mass proportion of the first graphite material is 90%, and the mass proportion of the second graphite material is 10%.

This embodiment also provides a negative electrode sheet, and the preparation method of the negative electrode sheet includes the following steps:

Mix the above-mentioned graphite material, binder and conductive agent, then add 3% water of the total mass of graphite material, binder and conductive agent, mix uniformly to prepare a slurry, and then coat the slurry on the negative electrode current collector copper foil The surface is dried, rolled and die-cut to obtain the negative electrode sheet.

Example 4

This embodiment provides a kind of negative electrode material, and described negative electrode material comprises graphite material, binding agent, conductive agent, and described graphite material is made of first graphite material (the first graphite material is selected from particle diameter D50 is 12 μm, and specific surface area is 1.2 m ² /g of artificial graphite, the artificial graphite is obtained by calcining needle coke for 21 days at 2800°C for graphitization, and then granulating), the second graphite material (the second graphite material is selected from the particle size D50 is 6 μm, specific surface area is 2.5m ² /g artificial graphite) composition, described binding agent is polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, and described conductive agent is conductive carbon black; The mass proportion of graphite material in the negative electrode material is 95.5%, the mass proportion of conductive agent is 1%, the mass proportion of polyacrylonitrile is 2.5%, the mass proportion of carboxymethyl cellulose sodium is 0.3%, styrene-butadiene The mass proportion of the rubber is 0.7%, wherein based on the total mass of the graphite material, the mass proportion of the first graphite material is 95%, and the mass proportion of the second graphite material is 5%.

This embodiment also provides a negative electrode sheet, and the preparation method of the negative electrode sheet includes the following steps:

Mix the above-mentioned graphite material, binder and conductive agent, then add 3% water of the total mass of graphite material, binder and conductive agent, mix uniformly to prepare a slurry, and then coat the slurry on the negative electrode current collector copper foil The surface is dried, rolled and die-cut to obtain the negative electrode sheet.

Example 5

The present embodiment provides a negative electrode material and a negative electrode sheet prepared therefrom. Compared with Example 1, the difference is that the binder is sodium carboxymethyl cellulose and styrene-butadiene rubber, and the quality of sodium carboxymethyl cellulose is The proportion is 1.0%, and the mass proportion of styrene-butadiene rubber is 2.5%.

Example 6

This embodiment provides a kind of negative electrode material, and described negative electrode material comprises graphite material, binding agent, conductive agent, and described graphite material is made of first graphite material (the first graphite material is selected from particle diameter D50 is 12 μm, and specific surface area is 1.2 m ² /g of artificial graphite, the artificial graphite is obtained by calcining needle coke for 21 days at 2800°C for graphitization, and then granulating), the second graphite material (the second graphite material is selected from the particle size D50 is 6 μ m, and specific surface area is 2.5m ² /g artificial graphite), described binding agent is polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, and described conductive agent is carbon nanotube; The mass proportion of graphite material in the negative electrode material is 95%, the mass proportion of conductive agent is 1.5%, the mass proportion of polyacrylonitrile is 2.5%, the mass proportion of carboxymethyl cellulose sodium is 0.3%, polyethylene The mass proportion of alcohol is 0.7%, wherein based on the total mass of the graphite material, the mass proportion of the first graphite material is 85%, and the mass proportion of the second graphite material is 15%.

This embodiment also provides a negative electrode sheet, and the preparation method of the negative electrode sheet includes the following steps:

Mix the above-mentioned graphite material, binder and conductive agent, then add 3% water of the total mass of graphite material, binder and conductive agent, mix uniformly to prepare a slurry, and then coat the slurry on the negative electrode current collector copper foil The surface is dried, rolled and die-cut to obtain the negative electrode sheet.

Example 7

This embodiment provides a kind of negative electrode material, and described negative electrode material comprises graphite material, binding agent, conductive agent, and described graphite material is made of first graphite material (the first graphite material is selected from particle diameter D50 is 12 μm, and specific surface area is 1.2 m ² /g of artificial graphite, the artificial graphite is obtained by calcining needle coke for 21 days at 2800°C for graphitization, and then granulating), the second graphite material (the second graphite material is selected from the particle size D50 is 6 μm, specific surface area is 2.5m ² /g artificial graphite), described binding agent is polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, and described conductive agent is Ketjen Black; The mass proportion of graphite material in the negative electrode material is 95%, the mass proportion of conductive agent is 1.5%, the mass proportion of polyacrylonitrile is 2.5%, the mass proportion of carboxymethyl cellulose sodium is 0.3%, styrene-butadiene The mass proportion of the rubber is 0.7%, wherein based on the total mass of the graphite material, the mass proportion of the first graphite material is 80%, and the mass proportion of the second graphite material is 20%.

This embodiment also provides a negative electrode sheet, and the preparation method of the negative electrode sheet includes the following steps:

Mix the above-mentioned graphite material, binder and conductive agent, then add 3% water of the total mass of graphite material, binder and conductive agent, mix uniformly to prepare a slurry, and then coat the slurry on the negative electrode current collector copper foil The surface is dried, rolled and die-cut to obtain the negative electrode sheet.

Example 8

This embodiment provides a negative electrode material and a negative electrode sheet thereof, which is different from the embodiment 1 in that styrene-butadiene rubber is replaced by fluorinated rubber.

Example 9

This embodiment provides a negative electrode material and a negative electrode sheet thereof, which is different from the embodiment 1 in that styrene-butadiene rubber is replaced by sodium alginate.

Comparative example 1

This comparative example provides a negative electrode material and a negative electrode sheet thereof, which is different from Example 1 in that the graphite material is only composed of the first graphite material without adding the second graphite material.

Comparative example 2

This comparative example provides a negative electrode material and its negative electrode sheet, which is different from Example 1 in that the graphite material is only composed of the second graphite material without adding the first graphite material.

test case 1

Take the negative electrode sheet prepared by the above-mentioned examples and comparative examples, and use the four-probe method to test the resistivity of the electrode sheet, and the test results are shown in Table 1:

Table 1 Resistivity of negative pole piece

Resistivity/Ω*cm Example 1 1.87 Example 2 1.71 Example 3 1.82 Example 4 1.93 Example 5 1.85 Example 6 1.69 Example 7 1.65 Example 8 1.86 Example 9 1.88 Comparative example 1 2.15 Comparative example 2 1.51

test case 2

Disperse LiNi _0.5 Co _0.2 Mn _0.3 O ₂ positive electrode material, carbon nanotubes, conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone according to the mass ratio of 96.5:1:0.5:2 to obtain the positive electrode slurry. The positive electrode slurry is coated on the surface of the aluminum foil of the positive electrode current collector, and the positive electrode sheet is obtained through drying, rolling, and die-cutting;

The negative electrode sheets prepared by the above-mentioned embodiments and comparative examples of the present invention were respectively used as battery negative electrode sheets;

Electrolyte solution: obtained by mixing ethylene carbonate, fluoroethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a mass ratio of 20:10:20:50.

The diaphragm is made of single-layer polyethylene (PE), and a 5Ah soft-pack lithium-ion battery is made by lamination process. The current discharge performance of the battery at different rates is tested. The test results are shown in Table 2.

Table 2 Battery discharge performance

Test case 3

The battery obtained in Test Example 2 was subjected to a charge-discharge cycle test at 25°C with a voltage range of 4.4-2.8V, and the results are shown in Table 3:

Table 3 Battery Cycle Test Performance

According to the above test results, it can be seen that after adding a specific second graphite material to the first graphite material, the resistivity of the electrode sheet becomes lower, thereby reducing the impedance of the battery, and the large-rate discharge capacity retention rate of the battery increases with the small particle graphite to a certain extent. Therefore, the power battery system adopted in the present invention can increase the power performance of the battery while ensuring the energy density of the battery. From the results in Table 3, it can be seen that after adding a certain proportion of the second graphite material, the cycle performance has no obvious effect. After adding a large proportion, the activity becomes larger and the side reactions increase and affect the cycle performance. When only the second graphite material is added, the battery cycle performance is relatively low. Difference.

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (10)

1. A negative electrode material, characterized in that the negative electrode material comprises a graphite material, a binder and a conductive agent; the graphite material comprises a first graphite material and a second graphite material; wherein the first graphite material is selected from the group consisting of a particle size D50 of 12 μm and a specific surface area of 1.2m ² Artificial graphite/g; the second graphite material is selected from the group consisting of a particle size D50 of 6 μm and a specific surface area of 2.5m ² Artificial graphite/g;

the binder is polyacrylonitrile, carboxymethyl cellulose salt and an aqueous binder;

the aqueous binder is selected from styrene-butadiene rubber.

2. The negative electrode material according to claim 1, wherein the artificial graphite in the first graphite material is obtained by calcining and graphitizing needle coke as a raw material and then granulating.

3. The anode material according to claim 2, wherein the calcination temperature is 2800 to 3200 ℃ and the calcination time is 18 to 25 days.

4. The negative electrode material according to claim 1, wherein the first graphite material has a mass ratio of 30 to 95% and the second graphite material has a mass ratio of 5 to 70% based on the total mass of the graphite materials.

5. The negative electrode material according to claim 4, wherein,

based on the total mass of the graphite materials, the mass ratio of the first graphite material is 70-90%, and the mass ratio of the second graphite material is 10-30%.

6. The negative electrode material according to claim 1, wherein the negative electrode material has a graphite material mass ratio of 70 to 99.9%, a binder mass ratio of 0.05 to 15%, and a conductive agent mass ratio of 0.05 to 15%.

7. The negative electrode material according to claim 1, wherein the negative electrode material comprises 0.5 to 5.0% by mass of polyacrylonitrile, 0.1 to 3.0% by mass of carboxymethyl cellulose salt, and 0.1 to 3.0% by mass of an aqueous binder;

the conductive agent is one or more selected from carbon nanotubes, graphene, conductive graphite, conductive carbon black, ketjen black and carbon fibers.

8. A negative electrode sheet, characterized in that the negative electrode sheet comprises a current collector and a negative electrode material supported on the current collector, the negative electrode material being the negative electrode material according to any one of claims 1 to 7.

9. The method for preparing the negative electrode sheet according to claim 8, comprising the steps of: and mixing graphite material, binder, conductive agent and water to prepare slurry, coating the slurry on the surface of a current collector, and drying, rolling and die cutting to obtain the negative plate.

10. The lithium ion battery is characterized by comprising a positive plate, a negative plate, a diaphragm and electrolyte, wherein the negative plate is prepared by the negative plate of claim 8 or the preparation method of claim 9.