WO2023029555A1

WO2023029555A1 - Negative electrode sheet, preparation method therefor, and application thereof

Info

Publication number: WO2023029555A1
Application number: PCT/CN2022/091731
Authority: WO
Inventors: 娄帅宾; 杨红新
Original assignee: 蜂巢能源科技股份有限公司
Priority date: 2021-08-30
Filing date: 2022-05-09
Publication date: 2023-03-09
Also published as: CN113675364B; CN113675364A

Abstract

The present disclosure relates to the technical field of lithium ion batteries, and relate in particular to a negative electrode sheet, a preparation method therefor, and an application thereof. The negative electrode sheet of the present disclosure comprises a current collector, a negative electrode slurry layer, and a plurality of graphene composite sheet layers; the negative electrode slurry layer is disposed on a surface of at least one side of the current collector, the graphene composite sheet layers are disposed on a surface of the negative electrode slurry layer on at least one side of the current collector, and the graphene composite sheet layers and the current collector are separately located on surfaces on both sides of the negative electrode slurry layer; each of the graphene composite sheet layers comprises at least two stacked graphene monolithic layers, and in the graphene composite sheet layers, the area of the graphene monolithic layers gradually decreases in the direction in which the negative electrode slurry layer is connected to away from the negative electrode slurry layer. The negative electrode sheet has functions of storing and releasing an electrolyte, the service life of a battery can be prolonged, bulging generated during the use of a cell can be alleviated, the safety performance is improved and usage costs of the cell are reduced.

Description

A kind of negative electrode sheet and its preparation method and application

Cross References to Related Applications

This application claims the priority of the Chinese patent application with the application number 2021110038749 and titled "A negative electrode sheet and its preparation method and application" submitted to the China Patent Office on August 30, 2021, the entire contents of which are incorporated herein by reference. Applying.

technical field

The present disclosure relates to the technical field of lithium-ion batteries, in particular, to a negative electrode sheet and its preparation method and application.

Background technique

With the increasing consumption of fossil fuels and the increasingly serious environmental pollution, clean energy and sustainable development have become the common goal of mankind. Reusable secondary batteries have entered people's field of vision and gradually penetrated into all walks of life in people's lives.

The rapid development of the automobile industry in recent years has brought great convenience to social development. As an important aspect of energy conservation and emission reduction, new energy vehicles have become more and more popular in daily life. Power batteries are the power source of new energy vehicles. more and more important. As an important part of the power battery, the negative electrode sheet has a very important impact on the lithium battery. At present, the negative electrode sheet of the lithium battery is mainly composed of graphite, silicon powder, conductive agent, binder, and solvent. The above materials are used in a certain proportion during the production process. Combined with a solvent, mixed and stirred at a high speed, and then evenly coated on the current collector to form a pole piece. The pole piece is made into a lithium battery by rolling, assembly, formation, capacity separation and other processes, which are used by people.

With the development of battery products, the performance requirements of batteries are getting higher and higher. The consumption of electrolyte during battery use will have a great impact on the service life of batteries, the charging and discharging capabilities of batteries, and the safety performance of batteries. Therefore, it is very important for the battery to maintain a certain amount of electrolyte in the battery. The main requirement of the above-mentioned coating method is uniform coating, and this coating method does not effectively improve the wetting ability of the electrolyte.

Therefore, there is an urgent need for a negative electrode sheet that improves electrolyte infiltration.

Contents of the invention

The present disclosure provides a negative electrode sheet, including a current collector, a negative electrode slurry layer, and a plurality of graphene composite sheets; the negative electrode slurry layer is arranged on the surface of at least one side of the current collector, and the graphene composite sheet A layer is disposed on the surface of the negative electrode slurry layer on at least one side of the current collector, and the graphene composite sheet and the current collector are separated on the surfaces of both sides of the negative electrode slurry layer;

Each of the graphene composite sheets includes at least two laminated graphene single sheets, and in the graphene composite sheets, the negative electrode slurry layer is connected to a direction away from the negative electrode slurry layer, The area of the graphene monolithic layer decreases gradually.

In some embodiments, the multiple graphene composite sheets are distributed in an A×B array on the surface of the negative electrode slurry layer;

Said A≥2, said B≥2, and both A and B are integers.

In some embodiments, in the A×B array, the distance between any two adjacent rows of graphene composite sheets is 1-60 mm.

In some embodiments, in the A×B array, the distance between any two adjacent rows of graphene composite sheets is 3-10 mm.

In some embodiments, a single graphene composite sheet includes 3-4 graphene single sheet layers.

In some embodiments, the thickness of a single graphene composite sheet is 2-4 nm.

In some embodiments, the specific surface area of a single graphene composite sheet is 200-260 m ² /g.

In some embodiments, the shape of the graphene monolithic layer includes at least one of rectangle, rhombus, square and circle.

In some embodiments, in the graphene composite sheet, the graphene single sheet of any upper layer is located at the center of the surface of the adjacent graphene single sheet of the lower layer.

In some embodiments, the current collector includes copper foil with a thickness of 4.5-10 μm.

In some embodiments, the negative electrode slurry layer is prepared from negative electrode slurry including graphite, conductive carbon black and a binder.

In some embodiments, the graphite includes at least one of artificial graphite, natural graphite, hard carbon and intermediate carbon microspheres.

In some embodiments, the conductive carbon black includes at least one of KS-6, Super PLI and superconducting carbon black.

In some embodiments, the binder includes sodium carboxymethylcellulose and/or styrene-butadiene rubber.

In some embodiments, the solid content of the negative electrode slurry is 40%-60%.

In some embodiments, the viscosity of the negative electrode slurry is 2000-7000 mPa.s.

The preparation method of described negative plate, comprises the following steps:

Coating negative electrode slurry on the surface of at least one side of the current collector, and drying to obtain the negative electrode slurry layer; coating the surface of the negative electrode slurry layer away from the current collector from bottom to top The graphene single sheet is obtained to obtain the graphene composite sheet.

A lithium ion battery comprises the negative electrode sheet, the positive electrode sheet and the electrolyte.

In some embodiments, the positive electrode sheet includes a positive electrode material, and the positive electrode material includes at least one of a nickel-cobalt-manganese ternary positive electrode material, lithium iron phosphate, and lithium manganate.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the accompanying drawings that need to be used in the embodiments. It should be understood that the following drawings are only illustrative of the embodiments of the present disclosure, and the size ratios in the drawings The true scale of the embodiments does not correspond directly, while the following figures only illustrate certain embodiments of the present disclosure and thus should not be considered as limiting the scope.

Fig. 1 is the schematic plan view of the structure of the negative plate in embodiment 1;

Fig. 2 is the schematic front view of negative plate structure in embodiment 1;

Fig. 3 is the schematic front view of negative plate structure in embodiment 5;

FIG. 4 is a graph showing the test results of the capacity retention rate of lithium-ion batteries in Example 6 and Comparative Example 1. FIG.

Reference signs:

1-collector, 2-negative electrode slurry layer, 201-first negative electrode slurry layer, 202-second negative electrode slurry layer, 3-first graphene composite sheet, 301-bottom first graphene single sheet layer , 302-the first graphene single sheet in the middle layer, 303-the first graphene single sheet in the upper layer, 4-the second graphene composite sheet, 401-the second graphene single sheet in the bottom layer, 402-the second graphite in the middle layer Graphene single sheet, 403-upper second graphene single sheet.

Detailed ways

The advantages of the embodiments in the summary of the invention will be explained in part of the embodiments in the following description, and part of them will be obvious from the description, or can be obtained through some of the embodiments of the present disclosure.

The technical solutions of the present disclosure will be further described below in conjunction with the accompanying drawings and through some implementation manners.

In order to make the purpose, technical solutions and advantages of the present disclosure clearer, the present disclosure will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments described here are only used to explain the present disclosure, not to limit the present disclosure. In addition, the technical features involved in the various embodiments of the present disclosure described below may be combined with each other as long as they do not constitute a conflict with each other. On the premise of not departing from the principles of the embodiments of the present disclosure, several improvements and modifications can also be made, and these improvements and modifications are also regarded as the protection scope of the embodiments of the present disclosure.

One embodiment provides a negative electrode sheet, including a current collector, a negative electrode slurry layer, and a plurality of graphene composite sheets; the negative electrode slurry layer is arranged on the surface of at least one side of the current collector, and the graphene composite sheet is arranged on the current collector On the surface of the negative electrode slurry layer on at least one side, and the graphene composite sheet and the current collector are separated on the surface of the negative electrode slurry layer on both sides;

Each graphene composite sheet comprises at least two laminated graphene monoliths, and in the graphene composite sheet, connects the negative electrode slurry layer to the direction away from the negative electrode slurry layer, the area of the graphene monolithic layer gradually decrease.

In the present disclosure, by arranging multiple graphene composite sheets on the negative electrode slurry layer of the negative electrode sheet, the graphene can quickly absorb the electrolyte into the graphene composite sheet. When the battery is used, as the number of applications of the battery increases, the battery The amount of internal electrolyte gradually decreases. At this time, the electrolyte stored in the graphene composite sheet is gradually released through diffusion to maintain the consumption of the internal electrolyte of the battery and ensure the normal use of the battery.

In some embodiments, the negative electrode slurry layer is arranged on the surface of both sides of the current collector to obtain the first negative electrode slurry layer and the second negative electrode slurry layer; the surface of the first negative electrode slurry layer away from the current collector is provided with a plurality of The first graphene composite sheet, and the surface of the second negative electrode slurry layer away from the current collector is provided with a plurality of second graphene composite sheets.

The above-mentioned structure of the negative plate can better store and release the electrolyte, prolong the service life of the battery, improve the bulging phenomenon during the use of the battery cell, and improve the safety performance.

In some embodiments, a plurality of graphene composite sheets are distributed in an A×B array on the surface of the negative electrode slurry layer;

A≥2, B≥2, and both A and B are integers.

By setting the graphene composite sheets with an array structure, the electrolyte can be better stored and released through the gully-like distribution, so as to maintain the consumption of the electrolyte inside the battery and ensure the normal use of the battery.

In some embodiments, in the A×B array, A is 5-10, and 6, 7, 8 or 9 can also be selected; B is 3-5, and 4 can also be selected.

In some embodiments, in the A×B array, the distance between any two adjacent rows of graphene composite sheets is 1 to 60mm, and 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm or 55mm.

In some embodiments, in the A×B array, the distance between any two adjacent rows of graphene composite sheets is 3-10 mm, and 4 mm, 5 mm, 6 mm, 7 mm, 8 mm or 9 mm can also be selected.

In the present disclosure, by setting the appropriate row spacing and column spacing of graphene composite sheets, it is more conducive to storing and releasing the electrolyte, ensuring the uniformity of electrolyte release, and more conducive to ensuring the normal operation of the battery and prolonging its service life.

In some embodiments, a single graphene composite sheet includes 3-4 graphene monosheets.

A single graphene composite sheet includes 2, 3 or 4 graphene monolayers.

In some embodiments, the thickness of a single graphene composite sheet is 2-4nm, and can also be selected from 2.1nm, 2.2nm, 2.3nm, 2.4nm, 2.5nm, 2.6nm, 2.7nm, 2.8nm, 2.9nm, 3nm, 3.1nm, 3.2nm, 3.3nm, 3.4nm, 3.5nm, 3.6nm, 3.7nm, 3.8nm or 3.9nm.

By setting a graphene composite sheet with an appropriate thickness, it can better release the stored electrolyte and ensure the normal operation of the battery.

In some embodiments, the specific surface area of a single graphene composite sheet is 200-260m ² /g, and can also be selected from 205m ² /g, 210m ² /g, 215m ² /g, 220m ² /g, 225m ² /g, 230m ² /g, 235m ² /g, 240m ² /g, 245m ² /g, 250m ² /g or 255m ² /g.

The shapes of the graphene single sheets in the graphene composite sheets are the same, or are superimposed combinations of the above-mentioned different shapes. The shape of the graphene monolithic layer may also include other parallelograms except rectangle, rhombus and square.

In some embodiments, in the graphene composite sheet, any upper graphene single sheet is located at the center of the surface of its adjacent lower graphene single sheet.

The above-mentioned graphene composite sheet structure is similar to a pyramid structure, and the structure has a stable arrangement. Using graphene's huge specific surface area and excellent liquid absorption and liquid retention performance, it slowly replenishes the electrolyte consumption of the battery cell and prolongs the battery life cycle.

In some embodiments, the thickness of the copper foil can also be selected as 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or 9.5 μm.

In some embodiments, the solid content of the negative electrode slurry can also be selected from 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, or 59%.

In some embodiments, the viscosity of the negative electrode slurry can also be selected from 2500mPa.s, 3000mPa.s, 3500mPa.s, 4000mPa.s, 4500mPa.s, 5000mPa.s, 5500mPa.s, 6000mPa.s, 6500mPa.s or 6800mPa .s.

The preparation method of the negative electrode sheet of one embodiment, comprises the following steps:

Coat the negative electrode slurry on the surface of at least one side of the current collector, and obtain the negative electrode slurry layer after drying; coat the graphene monolithic layer on the surface of the negative electrode slurry layer away from the current collector from bottom to top to obtain graphite vinyl composite sheet.

The preparation method of the negative plate in the present disclosure is simple and easy, safe and environmentally friendly, high in production efficiency, high in yield, and has good economic benefits. The negative electrode sheet prepared by the method can prolong the service life of the battery, reduce the use cost of the battery core, improve the swelling phenomenon generated during the use of the battery core, improve safety performance, and reduce the use cost of the battery core.

A lithium ion battery according to one embodiment includes the above negative electrode sheet, positive electrode sheet and electrolyte.

The lithium ion battery prepared by the negative electrode sheet of the present disclosure has a longer service life and higher safety performance.

The electrolyte used is any one or more combinations produced by Jinniu, Tianci, Xinzhoubang, and Luoyang Dasheng manufacturers.

In some embodiments, the positive electrode sheet includes a positive electrode material, and the positive electrode material includes at least one of nickel-cobalt-manganese ternary positive electrode material, lithium iron phosphate, and lithium manganese oxide.

The negative electrode sheet of the present disclosure can be combined with at least one of nickel-cobalt-manganese ternary positive electrode material, lithium iron phosphate and lithium manganate to prepare a lithium battery, that is, a nickel-cobalt-manganese battery, lithium iron phosphate battery or lithium manganate battery.

The following are typical but non-limiting embodiments of the present disclosure:

Example 1

A negative electrode sheet, comprising a current collector 1, a negative electrode slurry layer 2, a first graphene composite sheet 3 and a second graphene composite sheet 4, and one surface of the current collector 1 is provided with a first negative electrode slurry layer 201, The other surface of the current collector 1 is provided with a second negative electrode slurry layer 202; the first negative electrode slurry layer 201 is provided with a first graphene composite sheet 3 on the side surface of the first negative electrode slurry layer 201 away from the current collector 1, and the second negative electrode slurry layer 202 A second graphene composite sheet 4 is provided on the surface away from the current collector 1;

The first graphene composite sheet 3 comprises 3 laminated first graphene monosheets, namely the first graphene monosheet 301 at the bottom, the first graphene monosheet 302 in the middle layer and the first graphene monosheet at the top 303, and in any first graphene composite sheet 3, the area of the first graphene single sheet from the lower layer to the upper layer decreases layer by layer, the first graphene single sheet 301 of the bottom layer and the first negative electrode slurry layer 201 are connected; in the first graphene composite sheet 3, the first graphene single sheet of any upper layer is located at the center position of the first graphene single sheet surface of its adjacent lower layer;

The second graphene composite sheet 4 comprises 3 stacked second graphene monoliths, namely the second graphene monolith 401 at the bottom, the second graphene monolith 402 in the middle layer and the second graphene monolith at the top 403, and in the graphene composite sheet, the area of the second graphene monolithic layer from the bottom layer to the upper layer decreases layer by layer, and the second graphene monolithic layer 401 of the bottom layer is connected with the second negative electrode slurry layer 202; In the two graphene composite sheets 4, the second graphene single sheet of the upper layer is located at the center of the second graphene single sheet of the lower layer adjacent to it;

The first graphene composite sheet 3 is distributed in an A×B array on the surface of the first negative electrode slurry layer 201, wherein A is 10 and B is 5. In the A×B array, any two adjacent rows of the first The distance between the graphene composite sheets 3 is 5mm, and the distance between any adjacent two columns of the first graphene composite sheets 3 is 5mm; the second graphene composite sheets 4 are in the second negative electrode slurry layer 202 The surface of is in an A×B array, where A is 10 and B is 5. In the A×B array, the distance between any adjacent two rows of second graphene composite sheets 4 is 5 mm, and any adjacent two rows The distance between the second graphene composite sheet 4 is 5mm; the thickness of the single first graphene composite sheet 3 and the single second graphene composite sheet 4 is 3nm respectively, and the single first graphene composite sheet 3 and the specific surface area of a single second graphene composite sheet 4 are respectively 240m ² /g;

The first negative electrode slurry layer 201 and the second negative electrode slurry layer 202 are prepared from the mixed negative electrode slurry of graphite, conductive carbon black, binding agent and solvent; wherein, graphite is hard carbon, and conductive carbon black is KS -6, the binder is sodium carboxymethyl cellulose and styrene-butadiene rubber; the solid content of the negative electrode slurry is 50%, and the viscosity is 5000 mPa.s; the current collector 1 is copper foil with a thickness of 6 μm.

The schematic top view of the structure of the negative electrode sheet in the present embodiment is shown in Figure 1; the front view of the schematic structure of the negative electrode sheet in the present embodiment is shown in Figure 2.

The preparation method of the negative electrode sheet in the present embodiment comprises the following steps:

(a) Mix graphite, conductive carbon black, binder and solvent, and make a uniform slurry by high-speed stirring, apply the above-mentioned slurry on the two surfaces of the above-mentioned current collector 1, bake it with blast, evaporate After the excess solvent is removed, a uniform first negative electrode slurry layer 201 and a second negative electrode slurry layer 202 are formed;

(b) Replace the coating roller groove, with a certain coating speed and coating thickness, the graphene slurry is coated on the first negative electrode slurry layer 201 according to the above-mentioned A×B array, to form the first graphene unit in the bottom layer sheet layer 301, and then coat the first graphene monosheet layer 302 of the middle layer and the first graphene monosheet layer 303 of the upper layer successively; 401 , the second graphene single sheet layer 402 in the middle layer and the second graphene single sheet layer 403 in the upper layer.

Example 2

A negative electrode sheet, except that the first graphene composite sheet 3 includes 2 stacked first graphene single sheets, the second graphene composite sheet 4 includes 2 stacked first graphene single sheets, and the single first graphene sheet The thicknesses of a graphene composite sheet 3 and a single second graphene composite sheet 4 are respectively 2nm, and other conditions are the same as the negative electrode sheet in Example 1.

In the preparation method of the negative plate in the present embodiment, except that the first graphene composite sheet 3 of the two-layer structure and the second graphene composite sheet 4 of the two-layer structure are prepared in the step (b), other conditions are the same as those in Example 1 Preparation.

Example 3

A negative electrode sheet, except that the first graphene composite sheet 3 includes 4 stacked first graphene single sheets, and the second graphene composite sheet 4 includes 4 stacked first graphene single sheets. The thicknesses of a graphene composite sheet 3 and a single second graphene composite sheet 4 are respectively 4nm, and other conditions are the same as the negative electrode sheet in Example 1.

In the preparation method of the negative electrode sheet in the present embodiment, except that the first graphene composite sheet 3 and the second four-layer graphene composite sheet 4 of the four-layer structure are prepared in step (b), other conditions are the same as the preparation method of Example 1 .

Example 4

A negative electrode sheet, except that the first graphene composite sheet layer 3 is in an A×B array on the surface of the first negative electrode slurry layer 201, wherein A is 5, B is 3, and any two adjacent rows of first graphene The distance between the composite sheets 3 is 10 mm, and the second graphene composite sheet 4 is in an A×B array on the surface of the second negative electrode slurry layer 202, wherein A is 5, B is 3, and any adjacent two rows The distance between the second graphene composite sheets 4 is 10mm, and other conditions are the same as in Example 1.

In the preparation method of the negative plate in this embodiment, except that the arrays of the above-mentioned first graphene composite sheet 3 and the second graphene composite sheet 4 are different, and the row spacing and column spacing are different, other conditions are the same as those in Example 1. method.

Example 5

A negative electrode sheet, except that the second negative electrode slurry layer 202 and the second graphene composite sheet 4 are not provided, and other conditions are the same as the negative electrode sheet of embodiment 1.

The preparation method of the negative electrode sheet in this embodiment is the same as the preparation method of Embodiment 1 except that the second negative electrode slurry layer 202 and the second graphene composite sheet 4 are not provided.

The schematic front view of the structure of the negative electrode sheet in this embodiment is shown in FIG. 3 .

For the negative electrode sheet in the above-mentioned Examples 1-5, the thickness of the copper foil selected by the current collector 1 can also be 4.5 μm, 7 μm, 8 μm, 10 μm; the graphite can also be artificial graphite, natural graphite or intermediate carbon microspheres, conductive carbon Black can also be Super PLI or superconducting carbon black.

Example 6

A lithium-ion battery, comprising the negative electrode sheet, positive electrode sheet and electrolyte in embodiment 1; wherein, the positive electrode material of the positive electrode sheet is NCM613, and the chemical formula of NCM613 is LiNi _0.6 Co _0.1 Mn _0.3 O ₂ ;

The preparation method of lithium ion battery comprises the following steps:

The above-mentioned negative electrode sheet is rolled and made into sheets, assembled with the positive electrode sheet, and then injected with electrolyte solution, formed and separated to form a lithium-ion battery.

Comparative example 1

A kind of negative electrode sheet, except that graphene composite sheet is not set on the negative electrode sheet, other conditions are with embodiment 1;

A lithium ion battery, except that the negative electrode sheet in this comparative example is used, and other conditions are the same as in Example 6.

Test case

The lithium-ion batteries in Example 6 and Comparative Example 1 of the present disclosure were tested for capacity retention, and the results are shown in Table 1 and Figure 4; the test conditions were: 45°C, charging at 1C to 4.35V and then charging at constant voltage to 0.05C , 1C discharge to 2.8V, 100% DOD cycle.

In the present disclosure, by arranging multiple graphene composite sheets on the negative electrode slurry layer of the negative electrode sheet, the graphene can quickly absorb the electrolyte into the graphene composite sheet. When the battery is used, as the number of applications of the battery increases, the battery The amount of internal electrolyte gradually decreases. At this time, the electrolyte stored in the graphene composite sheet is gradually released through diffusion to maintain the consumption of the internal electrolyte of the battery and ensure the normal use of the battery. The lithium ion battery in Example 6 of the present disclosure has a more excellent capacity retention rate than the lithium ion battery in Comparative Example 1.

Table 1 Capacity retention results

Industrial Applicability

In summary, the present disclosure provides a negative electrode sheet, its preparation method and application. The negative electrode sheet of the present disclosure can prolong the service time of the battery and improve the bulging phenomenon during the use of the battery cell; the preparation method of the electrode sheet is simple and easy, safe and environmentally friendly, high in production efficiency, high in yield, and has excellent economic benefits.

Claims

A negative electrode sheet, characterized in that it includes a current collector, a negative electrode slurry layer and a plurality of graphene composite sheets; the negative electrode slurry layer is arranged on the surface of at least one side of the current collector, and the graphene composite The sheet layer is arranged on the surface of the negative electrode slurry layer on at least one side of the current collector, and the graphene composite sheet layer and the current collector are separated on the surfaces of both sides of the negative electrode slurry layer;

Each of the graphene composite sheets includes at least two laminated graphene single sheets, and in the graphene composite sheets, the negative electrode slurry layer is connected to a direction away from the negative electrode slurry layer, The area of the graphene monolithic layer decreases gradually.
The negative electrode sheet according to claim 1, wherein the plurality of graphene composite sheets are distributed in an A×B array on the surface of the negative electrode slurry layer;

Said A≥2, said B≥2, and both A and B are integers.
The negative electrode sheet according to claim 2, characterized in that, in the A×B array, the distance between any two adjacent rows of graphene composite sheets is 1-60 mm.
The negative electrode sheet according to claim 2 or 3, characterized in that, in the A×B array, the distance between any two adjacent rows of graphene composite sheets is 3-10 mm.
The negative electrode sheet according to any one of claims 1-4, characterized in that, the single graphene composite sheet layer comprises 3-4 graphene single sheet layers.
The negative electrode sheet according to any one of claims 1-5, characterized in that the thickness of a single graphene composite sheet is 2-4 nm.
The negative electrode sheet according to any one of claims 1-6, characterized in that the specific surface area of a single graphene composite sheet is 200-260 m 2 /g.
The negative electrode sheet according to any one of claims 1 to 7, wherein the shape of the graphene monolithic layer includes at least one of rectangle, rhombus, square and circle.
According to the negative electrode sheet according to any one of claims 1 to 8, it is characterized in that, in the graphene composite sheet, the graphene single sheet of any upper layer is located in the graphene single sheet of its adjacent lower layer. The center position of the sheet surface.
The negative electrode sheet according to any one of claims 1-9, characterized in that the current collector comprises copper foil with a thickness of 4.5-10 μm.
The negative electrode sheet according to any one of claims 1-10, characterized in that the negative electrode slurry layer is prepared from negative electrode slurry comprising graphite, conductive carbon black and a binder.
The negative electrode sheet according to claim 11, wherein the graphite comprises at least one of artificial graphite, natural graphite, hard carbon and intermediate carbon microspheres.
The negative electrode sheet according to claim 11 or 12, wherein said conductive carbon black comprises at least one of KS-6, Super PLI and superconducting carbon black.
The negative electrode sheet according to any one of claims 11-13, characterized in that the binder comprises sodium carboxymethylcellulose and/or styrene-butadiene rubber.
The negative electrode sheet according to any one of claims 11-14, characterized in that the solid content of the negative electrode slurry is 40%-60%.
The negative electrode sheet according to any one of claims 11-15, characterized in that the viscosity of the negative electrode slurry is 2000-7000 mPa.s.
The method for preparing a negative electrode sheet according to any one of claims 1 to 16, characterized in that it comprises the following steps:

Coating negative electrode slurry on the surface of at least one side of the current collector, and obtaining the negative electrode slurry layer after drying; coating from bottom to top on the surface of the negative electrode slurry layer away from the current collector The graphene single sheet is obtained to obtain the graphene composite sheet.
A lithium ion battery, characterized in that it comprises the negative electrode sheet, the positive electrode sheet and the electrolyte according to any one of claims 1-16.
The lithium ion battery according to claim 18, wherein the positive electrode sheet comprises a positive electrode material, and the positive electrode material includes at least one of nickel-cobalt-manganese ternary positive electrode material, lithium iron phosphate and lithium manganate.