Graphite negative plate, preparation method thereof and lithium ion battery

Abstract

The invention relates to a graphite negative plate and a preparation method thereof and a lithium ion battery, the preparation method comprises the following steps: mixing lithium hexafluorosilicate, a dopant and an organic solvent for ball milling, removing the organic solvent after ball milling, and then calcining in a protective atmosphere to obtain anion-doped lithium hexafluorosilicate, the dopant is selected from inorganic compounds containing anions in Cl <->, Br <-> and I <-> or anion groups in SO4 < 2->, PO4 < 3->, SeO4 < 2->, BO3 < 3->, HSO4 <->, H2PO4 <-> and HPO4 <->, and the mass ratio of the lithium hexafluorosilicate to the dopant is 1: 0.01-1: 0.1; and dispersing the anion-doped lithium hexafluorosilicate in an organic solvent to obtain a dispersion liquid, placing the dispersion liquid on the surface of the graphite material layer of the prefabricated graphite negative electrode plate, and drying to obtain the graphite negative electrode plate. The graphite negative plate obtained by the preparation method disclosed by the invention can effectively improve the fast charging capacity of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, in particular to a graphite negative electrode sheet and a preparation method thereof, and a lithium ion battery. Background Art

[0002] Graphite is the most typical negative electrode material for lithium-ion batteries. However, due to the inherent defects of its layered structure and the solvent effect of lithium ions during the cycle, the insertion, extraction and diffusion rates of lithium ions during the charge and discharge process are severely restricted, making it easy to cause serious lithium deposition and lithium dendrite growth during high current charge and discharge. Therefore, its fast charging performance is limited, which seriously restricts the development of lithium-ion batteries. Summary of the Invention

[0003] Based on this, it is necessary to provide a graphite negative electrode sheet and a preparation method thereof and a lithium-ion battery to address the above problems. The graphite negative electrode sheet obtained by the preparation method can effectively improve the fast charging capability of the lithium-ion battery.

[0004] A method for preparing a graphite negative electrode sheet comprises the following steps:

[0005] The lithium hexafluorosilicate, the dopant and the organic solvent are mixed and ball-milled, the organic solvent is removed after the ball-milling, and then calcined under a protective atmosphere to obtain anion-doped lithium hexafluorosilicate, wherein the dopant is selected from the group consisting of Cl - Br - , I - Anions or SO4 2- PO4 3- 、SeO4 2- , BO3 3- 、HSO4 - 、H2PO4 - 、HPO4 - An inorganic compound containing an anionic group, wherein the mass ratio of the lithium hexafluorosilicate to the dopant is 1:0.01-1:0.1;

[0006] dispersing the anion-doped lithium hexafluorosilicate in an organic solvent to obtain a dispersion;

[0007] A prefabricated graphite negative electrode sheet is provided, which includes a current collector and a graphite material layer attached to the surface of the current collector. The dispersion is placed on the surface of the graphite material layer of the prefabricated graphite negative electrode sheet, and the graphite negative electrode sheet is obtained after drying.

[0008] In one embodiment, the dopant is selected from ammonium salts.

[0009] In one embodiment, the dopant is selected from at least one of NH4Cl, NH4Br, NH4I, (NH4)2SO4, NH4HSO4, NH4H2PO4, (NH4)2HPO4, (NH4)3PO4, (NH4)2SeO4, and (NH4)3BO3.

[0010] In one embodiment, in the step of mixing lithium hexafluorosilicate, a dopant and an organic solvent for ball milling, the boiling point of the organic solvent is 60° C.-100° C. and the viscosity is 0.3 mPa·s-5 mPa·s.

[0011] In one embodiment, the ball milling speed is 500 r / min-1500 r / min, and the time is 2 h-8 h.

[0012] In one embodiment, the organic solvent is removed by vacuum drying.

[0013] In one embodiment, the calcination temperature is 200° C.-400° C., and the heat treatment time is 4 h-8 h.

[0014] A graphite negative electrode sheet obtained by the preparation method comprises a current collector and a graphite material layer attached to the surface of the current collector, and an anion-doped lithium hexafluorosilicate layer is also attached to the surface of the graphite material layer.

[0015] In one embodiment, the mass of the anion-doped lithium hexafluorosilicate layer is 2 to 10 times the mass of the graphite in the graphite material layer.

[0016] A lithium-ion battery uses the graphite negative electrode sheet.

[0017] In the preparation method of the present invention, when the lithium hexafluorosilicate host material and the dopant are ball-milled, the mechanical shear force generated by the ball milling will destroy the inherent lattice of the host material, increase its lattice defects and surface active sites, and at the same time, the heat generated by the ball milling in the liquid phase system can accelerate the process of ion exchange or adsorption competition, promote the diffusion and mixing of ions, and facilitate the exchange of anions or anionic groups. Then, combined with calcination, the doping of lithium hexafluorosilicate with anions can be achieved.

[0018] Furthermore, the doped anions can change the crystal structure of the host material, lithium hexafluorosilicate, thereby increasing or promoting the pathway and rate of ion diffusion. At the same time, the introduction of anions can further change the electric field and electron cloud density distribution within lithium hexafluorosilicate, not only reducing the migration energy barrier of lithium ions, but also accelerating the rate of their directional migration. Therefore, when applied to graphite negative electrodes, it can not only effectively promote the rapid transmission of lithium ions, but also reduce electrochemical polarization, improve the overall stability of the graphite negative electrode, and further improve the lithium insertion kinetics of the graphite negative electrode, thereby improving the fast charging capability of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 This is the first cycle GCD curve of the button cell of Example 5 at 0.1C;

[0021] Figure 2 This is the first cycle GCD curve of the button battery of Comparative Example 1 at 0.1C;

[0022] Figure 3 This is the first cycle GCD curve of a blank button battery at 0.1C. DETAILED DESCRIPTION

[0023] To facilitate understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or the combination of all related listed items.

[0025] In the present invention, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0026] The method for preparing a graphite negative electrode sheet provided by the present invention comprises the following steps:

[0027] S11, mixing lithium hexafluorosilicate, a dopant and an organic solvent and ball milling, removing the organic solvent after the ball milling, and then calcining under a protective atmosphere to obtain anion-doped lithium hexafluorosilicate, wherein the dopant is selected from the group consisting of Cl - Br - , I - Anions or SO4 2- PO4 3- 、SeO4 2- , BO3 3- 、HSO4 - 、H2PO4 - 、HPO4 - An inorganic compound containing an anionic group, wherein the mass ratio of the lithium hexafluorosilicate to the dopant is 1:0.01-1:0.1;

[0028] S12, dispersing the anion-doped lithium hexafluorosilicate in an organic solvent to obtain a dispersion;

[0029] S13, providing a prefabricated graphite negative electrode sheet, wherein the prefabricated graphite negative electrode sheet includes a current collector and a graphite material layer attached to the surface of the current collector, placing the dispersion on the surface of the graphite material layer of the prefabricated graphite negative electrode sheet, and obtaining a graphite negative electrode sheet after drying.

[0030] In step S11, when the lithium hexafluorosilicate host material and the dopant are ball-milled, the mechanical shear force generated will destroy the inherent lattice of the host material, increase its lattice defects and surface active sites, and at the same time, the heat generated by ball milling in the liquid phase system can accelerate the process of ion exchange or adsorption competition, promote the diffusion and mixing of ions, and facilitate the exchange of anions or anionic groups.

[0031] In addition, by controlling the mass ratio of the lithium hexafluorosilicate to the dopant to 1:0.01-1:0.1, for example, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, etc., or a range consisting of any two of these values, it is not only beneficial to maintain the intrinsic characteristics of lithium hexafluorosilicate and optimize the ion / electron transmission path, but also to avoid lattice distortion and maintain the stability of the material.

[0032] Optionally, the ball milling speed is preferably 500r / min-1500r / min, for example, 500r / min, 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, 1100r / min, 1200r / min, 1300r / min, 1400r / min, 1500r / min, etc., or a range consisting of any two of these values, and the ball milling time is preferably 2h-8h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc., or a range consisting of any two of these values.

[0033] Since ammonium salts are easily decomposed by heat, the dopant is selected from ammonium salts to avoid introducing other elements that may affect the performance of anion-doped lithium hexafluorosilicate. Furthermore, the dopant is preferably selected from at least one of NH4Cl, NH4Br, NH4I, (NH4)2SO4, NH4HSO4, NH4H2PO4, (NH4)2HPO4, (NH4)3PO4, (NH4)2SeO4, and (NH4)3BO3.

[0034] In order to better disperse lithium hexafluorosilicate and dopants during the ball milling process, while taking into account the wettability of lithium hexafluorosilicate and dopants and the ball milling efficiency, an organic solvent with a boiling point of 60°C-100°C and a viscosity of 0.3mPa·s-5mPa·s at room temperature is preferred. Optionally, the organic solvent is selected from at least one of methanol, ethanol, acetone, tetrahydrofuran, acetonitrile, cyclohexane, n-hexane, and isopropanol.

[0035] After ball milling, a small amount of organic solvent will generally remain. In order to avoid environmental interference, the present invention preferably uses vacuum drying to remove the organic solvent, wherein the vacuum drying temperature is preferably 80°C-120°C, and the time is preferably 8h-12h.

[0036] After vacuum drying, the calcination process further decomposes unstable dopants, avoiding local concentration and achieving a uniform doping concentration. Simultaneously, the high temperature environment further eliminates stress and strain caused by anion doping, promoting stable anion doping and producing anion-doped lithium hexafluorosilicate.

[0037] It should be noted that when the dopant contains SO4 2- PO4 3- 、SeO4 2- , BO3 3- 、HSO4 - 、H2PO4 - 、HPO4 - When an inorganic compound contains anionic groups, the anionic groups will further decompose during the calcination process, and the final doping is anion.

[0038] In the calcination step, the protective atmosphere is preferably an inert atmosphere such as nitrogen and argon. The calcination temperature can be controlled according to the dopant to ensure that the dopant can be decomposed. Preferably, the calcination temperature is 200°C-400°C and the heat treatment time is 4h-8h.

[0039] Optionally, the organic solvent described in step S12 is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, dimethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, acetonitrile, butyronitrile, benzonitrile, ethanedinitrile or acrylonitrile.

[0040] It can be understood that the prefabricated graphite negative electrode sheet in step S13 is a traditional graphite negative electrode sheet, which is prepared by mixing components such as graphite, a conductive agent and a binder to form a slurry, and then coating the slurry on a current collector and drying and slicing it. The present invention mainly uses anion-doped lithium hexafluorosilicate on the traditional graphite negative electrode sheet for treatment to improve the fast charging performance of the graphite negative electrode sheet.

[0041] In addition, the dispersion liquid may be placed on the surface of the graphite material layer of the prefabricated graphite negative electrode sheet by coating, dripping, or the like.

[0042] Furthermore, the present invention provides a graphite negative electrode sheet prepared using the above-described method, comprising a current collector and a graphite material layer attached to the surface of the current collector, wherein the surface of the graphite material layer further comprises an anion-doped lithium hexafluorosilicate layer. The graphite material layer is made of graphite, a binder, a conductive agent, and the like in a suitable proportion.

[0043] In the anion-doped lithium hexafluorosilicate prepared by the present invention, the doped anions can change the crystal structure of the host material lithium hexafluorosilicate to increase or promote the path and rate of ion diffusion. At the same time, the introduction of anions can further change the distribution of the electric field and electron cloud density inside the lithium hexafluorosilicate, which can not only reduce the migration energy barrier of lithium ions, but also accelerate the rate of their directional migration.

[0044] Therefore, when the anion-doped lithium hexafluorosilicate of the present invention is applied to the graphite negative electrode sheet, it can not only effectively promote the rapid transmission of lithium ions, but also reduce electrochemical polarization, improve the overall stability of the graphite negative electrode sheet, and further improve the lithium insertion kinetics process of the graphite negative electrode sheet, thereby improving the fast charging capability of the lithium-ion battery.

[0045] Optionally, the mass of the anion-doped lithium hexafluorosilicate layer is 2 to 10 times the mass of the graphite in the graphite material layer.

[0046] Furthermore, the present invention also provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet is the graphite negative electrode sheet described in the present invention.

[0047] Hereinafter, the graphite negative electrode sheet, its preparation method and lithium-ion battery will be further described through the following specific examples.

[0048] Blank example

[0049] Weigh 320 mg of artificial graphite material, 40 mg of conductive carbon black and 40 mg of carboxymethyl cellulose, add appropriate amount of deionized water and use planetary ball mill to mill for 2 h. The milled slurry is coated on the copper foil current collector and vacuum dried at 80 ° C for 12 h. Then, cut into graphite negative electrode sheets with a diameter of 12 mm and a loading of 2.5 mg / cm 2 .

[0050] Then, metallic lithium was used as the counter electrode and reference electrode, PP membrane was selected as the diaphragm, LiPF6 with a concentration of 1 mol / L was used as the electrolyte, and the solvent was a mixed solution of diethyl carbonate and ethylene carbonate with a volume ratio of 1:1. The button battery was assembled in a glove box with an argon atmosphere.

[0051] Comparative Example 1

[0052] Weigh 12 g of lithium hydroxide and 36 g of fluorosilicic acid, first dissolve the lithium hydroxide in 50 mL of deionized water, then add fluorosilicic acid and drop an appropriate amount of hydrofluoric acid to assist in regulating the pH value of the solution to 2 to ensure the smooth progress of the reaction, and control the reaction temperature at 100 ° C., react for 2 hours, then filter and wash the reaction product several times, and heat it to 200 ° C. at a heating rate of 5 ° C / min under a nitrogen atmosphere, keep it warm for 2 hours, and then cool to room temperature to prepare lithium hexafluorosilicate.

[0053] The lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 500 μL of the dispersion was evenly applied to the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0054] Example 1

[0055] 10.0 g of the lithium hexafluorosilicate prepared in Comparative Example 1 and 0.1 g of ammonium chloride (NH4Cl) were placed in a ball mill. 30 mL of ethanol was added and the mixture was ball milled at 500 rpm for 2 hours. The mixture was then vacuum dried at 100°C for 10 hours and finally calcined at 300°C under nitrogen for 2 hours to obtain chloride-doped lithium hexafluorosilicate.

[0056] The chloride-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of chloride-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 300 μL of the dispersion was evenly applied to the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0057] Example 2

[0058] 10.0 g of lithium hexafluorosilicate prepared in Comparative Example 1 and 0.2 g of ammonium bromide (NH4Br) were placed in a ball mill. 30 mL of ethanol was added and the mixture was ball milled at 500 rpm for 4 hours. The mixture was then vacuum dried at 100°C for 10 hours and finally calcined at 300°C under nitrogen for 2 hours to obtain bromide-doped lithium hexafluorosilicate.

[0059] The chloride-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of bromide-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 500 μL of the dispersion was evenly applied to the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0060] Example 3

[0061] 10.0 g of the lithium hexafluorosilicate prepared in Comparative Example 1 and 0.2 g of ammonium iodide (NH₄I) were placed in a ball mill. 30 mL of ethanol was added and the mixture was ball milled at 500 rpm for 4 hours. The mixture was then vacuum dried at 100°C for 10 hours and finally calcined at 300°C under nitrogen for 2 hours to obtain iodine-doped lithium hexafluorosilicate.

[0062] The chloride-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of iodine-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 800 μL of the dispersion was evenly applied to the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0063] Example 4

[0064] 10.0 g of lithium hexafluorosilicate prepared in Comparative Example 1 and 0.3 g of ammonium dihydrogen phosphate (NH₄H₂PO₄) were placed in a ball mill. 30 mL of dimethylformamide was added and the mixture was ball milled at 800 rpm for 4 hours. The mixture was then vacuum dried at 120°C for 10 hours and calcined at 300°C under nitrogen for 2 hours to obtain phosphorus-doped lithium hexafluorosilicate.

[0065] The phosphorus-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of phosphorus-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 500 μL of the dispersion was evenly drop-coated on the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0066] Example 5

[0067] 10.0 g of lithium hexafluorosilicate prepared in Comparative Example 1 and 0.6 g of diammonium hydrogen phosphate ((NH₄)₂HPO₄) were placed in a ball mill. 30 mL of dimethylformamide was added and the mixture was ball milled at 1000 rpm for 4 hours. The mixture was then vacuum dried at 120°C for 10 hours and calcined at 350°C under nitrogen for 2 hours to obtain phosphorus-doped lithium hexafluorosilicate.

[0068] The phosphorus-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of phosphorus-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 500 μL of the dispersion was evenly drop-coated on the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0069] Example 6

[0070] 10.0 g of lithium hexafluorosilicate prepared in Comparative Example 1 and 0.8 g of ammonium dihydrogen phosphate (NH₄H₂PO₄) were placed in a ball mill. 30 mL of dimethylformamide was added and the mixture was ball milled at 1500 rpm for 4 hours. The mixture was then vacuum dried at 100°C for 10 hours and calcined at 350°C under nitrogen for 2 hours to obtain phosphorus-doped lithium hexafluorosilicate.

[0071] The phosphorus anion-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of phosphorus anion-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 500 μL of the dispersion was evenly applied to the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0072] Example 7

[0073] 10.0 g of lithium hexafluorosilicate prepared in Comparative Example 1 and 0.8 g of ammonium phosphate (NH₄)₃PO₄) were placed in a ball mill. 30 mL of dimethylformamide was added and the mixture was ball milled at 1000 rpm for 4 hours. The mixture was then vacuum dried at 120°C for 10 hours and calcined at 400°C under nitrogen for 2 hours to obtain phosphorus-doped lithium hexafluorosilicate.

[0074] The phosphorus anion-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of phosphorus anion-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 500 μL of the dispersion was evenly applied to the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0075] Example 8

[0076] 10.0 g of lithium hexafluorosilicate prepared in Comparative Example 1 and 0.6 g of ammonium sulfate ((NH₄)₂SO₄) were placed in a ball mill. 30 mL of dimethylformamide was added and the mixture was ball milled at 1000 rpm for 4 hours. The mixture was then vacuum dried at 120°C for 10 hours and calcined at 400°C under nitrogen for 2 hours to obtain sulfur-doped lithium hexafluorosilicate.

[0077] The sulfur-ion-doped lithium hexafluorosilicate obtained above was evenly dispersed in an acetonitrile solution to obtain a dispersion. The concentration of sulfur-ion-doped lithium hexafluorosilicate in the dispersion was 0.05 g / ml. 500 μL of the dispersion was evenly applied to the surface of a blank graphite negative electrode sheet. The sheet was then dried at 80°C and assembled into a button cell using the same method as the blank.

[0078] The electrochemical performance test of the button cell obtained above was carried out on a Xinwei battery test system. The charge and discharge voltage range was 0.005V-2V, the current density was 0.1C, and 1C=372 mA / g. The test results are as follows: Figures 1 to 3 and as shown in Table 1.

[0079] Table 1

[0080]

[0081] Combine Figures 1 to 3 As shown in Table 1, the anion-doped lithium hexafluorosilicate prepared by the present invention shows higher ionic conductivity before and after battery cycling, indicating that it improves the ion / electron transmission rate of the graphite negative electrode and greatly improves the cycle stability of graphite fast charging (3C).

[0082] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a graphite negative electrode sheet, characterized in that: The following steps are involved: The lithium hexafluorosilicate, the dopant and the organic solvent are mixed and ball-milled, the organic solvent is removed after the ball-milling, and then calcined under a protective atmosphere to obtain anion-doped lithium hexafluorosilicate, wherein the dopant is selected from the group consisting of Cl - Br - , I - Anions or SO4 2- PO4 3- 、SeO4 2- , BO3 3- 、HSO4 - 、H2PO4 - 、HPO4 - An inorganic compound containing an anionic group, wherein the mass ratio of the lithium hexafluorosilicate to the dopant is 1:0.01-1:0.1; dispersing the anion-doped lithium hexafluorosilicate in an organic solvent to obtain a dispersion; A prefabricated graphite negative electrode sheet is provided, which includes a current collector and a graphite material layer attached to the surface of the current collector. The dispersion is placed on the surface of the graphite material layer of the prefabricated graphite negative electrode sheet, and the graphite negative electrode sheet is obtained after drying.

2. The method for preparing a graphite negative electrode sheet according to claim 1, wherein: The dopant is selected from ammonium salts.

3. The method for preparing a graphite negative electrode sheet according to claim 2, wherein: The dopant is selected from at least one of NH4Cl, NH4Br, NH4I, (NH4)2SO4, NH4HSO4, NH4H2PO4, (NH4)2HPO4, (NH4)3PO4, (NH4)2SeO4, and (NH4)3BO3.

4. The method for preparing a graphite negative electrode sheet according to claim 1, wherein: In the step of mixing lithium hexafluorosilicate, a dopant and an organic solvent for ball milling, the boiling point of the organic solvent is 60° C.-100° C. and the viscosity is 0.3 mPa·s-5 mPa·s.

5. The method for preparing a graphite negative electrode sheet according to claim 1, wherein: The ball mill has a rotation speed of 500 r / min-1500 r / min and a time of 2 h-8 h.

6. The method for preparing a graphite negative electrode sheet according to claim 1, wherein: The organic solvent is removed by vacuum drying.

7. The method for preparing a graphite negative electrode sheet according to claim 1, wherein: The calcination temperature is 200° C.-400° C., and the heat treatment time is 4 h-8 h.

8. A graphite negative electrode sheet obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The invention comprises a current collector and a graphite material layer attached to the surface of the current collector, and an anion-doped lithium hexafluorosilicate layer is further attached to the surface of the graphite material layer.

9. The graphite negative electrode sheet according to claim 8, characterized in that: The mass of the anion-doped lithium hexafluorosilicate layer is 2 to 10 times the mass of the graphite in the graphite material layer.

10. A lithium ion battery, characterized in that: The graphite negative electrode sheet as claimed in claim 9 is used.

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