Fluorine-doped graphite material, and preparation method and application thereof

Abstract

The application discloses a fluorine-doped graphite material and a preparation method and application thereof, and belongs to the technical field of energy storage materials. The preparation method of the fluorine-doped graphite material comprises the following steps: mixing graphite powder and fluorine source powder to obtain preliminary materials; the mass ratio of the graphite powder to the fluorine source powder is (1-20):1; and the preliminary materials are subjected to heat treatment at 300-800 DEG C to obtain the fluorine-doped graphite material. The graphite negative electrode material prepared by using the solid-phase fluorination method is significantly superior to the non-fluorinated graphite in terms of the first coulomb efficiency, cycle stability and rate performance. This shows that the solid-phase fluorination method is an effective and practical modification method of the graphite negative electrode material and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a fluorine-doped graphite material and a preparation method and application thereof. BACKGROUND

[0002] Graphite is widely used as an anode material for lithium-ion batteries due to its high theoretical specific capacity, good cycle stability, and low cost. However, graphite has a large irreversible capacity loss during the first charge-discharge process, and its performance decreases at high rates. To address these issues, researchers have attempted to modify graphite through various methods, with fluorination being an effective approach. Fluorination can improve the surface properties of graphite, increase the initial coulombic efficiency, and enhance the cycle stability and rate performance. Patent CN117855441A discloses a fluorine-doped graphite anode material prepared by sintering a fluorine source organic compound with an amine organic compound. This material can improve the fast-charging performance of lithium-ion batteries while maintaining high energy density and cycle performance. However, this method uses organic fluorides and amine compounds, which are expensive raw materials. Precise control equipment and reaction devices are required to ensure accurate control of reaction conditions, increasing equipment investment. Therefore, there is a need for a lower-cost fluorine-doping method suitable for low-cost, high-volume industrial production. SUMMARY

[0003] The present application aims to solve the problems of high cost and complex process of existing graphite fluorination methods, and provides a fluorine-doped graphite material, a preparation method and application thereof. The method is simple and low-cost, and the prepared fluorine-doped graphite anode material has good electrochemical performance.

[0004] The present application solves the above technical problems through the following technical solutions:

[0005] The present application provides a preparation method of a fluorine-doped graphite material, comprising the following steps:

[0006] Mixing graphite powder with fluorine source powder to obtain preliminary material; the mass ratio of the graphite powder to the fluorine source powder is (1-20):1;

[0007] Heat-treating the preliminary material at 300-800°C to obtain a fluorine-doped graphite material.

[0008] In the present application, the mixing is preferably carried out by ball milling. The ball milling is conventional in the art.

[0009] In some embodiments, the ball mill has a rotation speed of 200-500 r / min, such as 300 r / min, 350 r / min or 400 r / min.

[0010] In some embodiments, the ball milling time is 10-25 hours, such as 10 hours, 12 hours, 18 hours, 20 hours, 24 hours, and 30 hours.

[0011] In some embodiments, the ball milling ball-to-material ratio is (10-20):1, such as 15:1 or 20:1.

[0012] In some embodiments, the ball milling grinding body is a stainless steel ball or a ceramic ball.

[0013] In some embodiments, the mass ratio of the graphite powder to the fluorine source powder is (2-10):1, preferably (2-3):1, such as 2:1, 2.5:1, 3.3:1, 5:1, or 10:1.

[0014] When the mass ratio of the graphite powder to the fluorine source powder is too low (e.g., 1:43), the fluorination degree is very high, which can cause over-fluorination, unstable structure, low initial coulombic efficiency, loose material structure, poor cycle stability, low conductivity, and poor rate performance. When the mass ratio of the graphite powder to the fluorine source powder is too high (e.g., 100:1), the fluorination degree is low, which can cause incomplete fluorination, large irreversible capacity loss, low initial coulombic efficiency, large volume expansion during charge and discharge, poor cycle stability, low lithium ion diffusion rate, high internal resistance, and high charge transfer resistance. Therefore, the mass ratio range of the present application is preferred.

[0015] In some embodiments, the fluorine source powder is an inorganic fluorine source, preferably, the inorganic fluorine source is KF, CaF2, NH4F, or K2MnF6, preferably KF, CaF2, or NH4F.

[0016] In some embodiments, the D50 particle size of the fluorine source powder is 5-20 μm, such as 7.9 μm, 10.1 μm, 12 μm, 12.3 μm, 13.9 μm, 14.7 μm, 15.3 μm, or 15.7 μm.

[0017] In some embodiments, the graphite powder is a natural graphite powder or a synthetic graphite powder.

[0018] In some embodiments, the D50 particle size of the graphite powder is 5-20 μm, such as 5.1 μm, 6.5 μm, 7.4 μm, 8 μm, 8.4 μm, 9.2 μm, or 10.3 μm; preferably, the standard deviation (SD) of the particle size distribution of the graphite powder is less than 3 μm.

[0019] Suitable graphite particle size makes the graphite have a large specific surface area while being conducive to improving the fluorination degree and uniformity. If the particle size is too large, the fluorination reaction is non-uniform, leading to poor consistency of the properties of the fluorinated graphite. If the particle size is too small (e.g., 2-5 μm), although the first coulombic efficiency and rate performance can be improved to some extent, the cycle stability is reduced, and the complexity of the graphite processing process is increased.

[0020] In some embodiments, the graphite powder has a crystallinity greater than 95%, such as 96.3%.

[0021] In some embodiments, the graphite powder has a purity greater than 99.9%.

[0022] In some embodiments, the heat treatment is performed at a temperature of 500-700°C, preferably 700°C, such as 300°C, 400°C, 500°C, 600°C, 700°C, or 800°C.

[0023] In some embodiments, the heat treatment is performed for a time of 1-10 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h.

[0024] In some embodiments, the heat treatment is performed in an inert atmosphere, preferably argon or nitrogen.

[0025] In some embodiments, the heat treatment is performed using equipment conventional in the art, such as a muffle furnace or a tube furnace.

[0026] In some embodiments, the heat treatment further comprises a cooling, washing, and drying step after the heat treatment.

[0027] The cooling, washing, and drying steps are conventional in the art.

[0028] In some embodiments, the cooling step comprises natural cooling to room temperature.

[0029] In some embodiments, "room temperature" refers to 10-30°C.

[0030] In some embodiments, the washing is performed using deionized water or ethanol to remove unreacted fluorine source and other impurities, preferably the washing is performed 2-5 times.

[0031] In some embodiments, the drying is performed at a temperature of 60-100°C, such as 60°C, 70°C, 80°C, and 90°C, and preferably the drying is performed for a time of 10-25 h, such as 10 h, 12 h, 16 h, 20 h, and 24 h.

[0032] The present application also provides a fluorine-doped graphite material prepared by the method described above.

[0033] The fluorine-doped graphite material of the present application is a layered compound, and fluorine atoms are intercalated between the layers of graphite. After fluorination, the interlayer spacing of graphite increases from 0.335 nm for unfluorinated graphite to about 0.35-0.40 nm for fluorinated graphite.

[0034] The present application also provides a use of the aforementioned fluorine-doped graphite material as a negative electrode material in a lithium-ion battery.

[0035] The positive progress effect of the present application is that:

[0036] (1) The graphite negative electrode material prepared by the solid-phase fluorination method is significantly superior to unfluorinated graphite in terms of initial coulombic efficiency, cycle stability, and rate performance. This indicates that the solid-phase fluorination method is an effective and practical modification method for graphite negative electrode materials, and has broad application prospects.

[0037] (2) Fluorination treatment significantly improves the specific capacity of the graphite negative electrode material. The discharge capacity of all examples at various rates is higher than that of unfluorinated Comparative Example 1, which indicates that fluorination treatment can effectively increase the lithium ion intercalation amount of the material and improve the lithium storage capacity of the material.

[0038] Fluorination treatment significantly improves the rate performance of the graphite negative electrode material, especially at high rates (2C and 5C), the discharge capacity of the examples is significantly higher than that of Comparative Example 1. This indicates that fluorination treatment can improve the electrical conductivity and lithium ion diffusion rate of the material, and improve the performance of the material under high-rate charge and discharge conditions.

[0039] Fluorination treatment improves the initial coulombic efficiency of the material and reduces the irreversible capacity loss, which is particularly evident at low rates (0.1C and 0.5C). This indicates that fluorination treatment can improve the surface properties of the material, reduce side reactions, and improve the electrochemical stability of the material.

[0040] (3) Fluorination treatment significantly reduces the internal resistance of the graphite negative electrode material. The DCIR of all examples is lower than that of unfluorinated Comparative Example 1, which indicates that fluorination treatment can effectively improve the electrical conductivity of the material and reduce the energy loss inside the battery.

[0041] Fluorination treatment significantly reduces the charge transfer resistance, improves the electrochemical reactivity of the material, improves the electrical conductivity of the material, reduces the solution resistance, reduces the diffusion resistance of lithium ions in the material, and improves the diffusion rate of lithium ions. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 SEM image of fluorinated graphite. DETAILED DESCRIPTION

[0043] The present application is further illustrated by the following examples without thereby limiting the present application to the scope of the examples. The experimental methods in the following examples, unless otherwise specified, are carried out according to the conventional methods and conditions, or according to the commercial instructions.

[0044] The graphite powder used in the following examples and comparative examples has a crystallinity of 96.3% and a purity of 99.96%.

[0045] Example 1

[0046] (1) 10 g of natural graphite powder (D50 particle size of 6.5 μm) and 5 g of KF (D50 particle size of 15.3 μm) were weighed.

[0047] (2) The graphite powder and KF were put into a ball mill tank, an appropriate amount of stainless steel balls were added, and the ball-to-material ratio was 15:1. Ball milling was carried out in a ball mill for 24 hours at a rotation speed of 300 r / min.

[0048] (3) The mixed powder was uniformly spread in a crucible, and was put into a muffle furnace for heat treatment at 500 °C for 4 hours in an argon atmosphere.

[0049] (4) After natural cooling to room temperature, the product was washed with deionized water for 3 times, and then was dried at 80 °C for 12 hours to obtain the fluorinated graphite.

[0050] Example 2

[0051] (1) 10 g of artificial graphite (D50 particle size of 10.3 μm) and 3 g of CaF2 (D50 particle size of 12 μm) were weighed.

[0052] (2) The graphite powder and CaF2 were put into a ball mill tank, an appropriate amount of ceramic balls were added, and the ball-to-material ratio was 15:1. Ball milling was carried out in a ball mill for 12 hours at a rotation speed of 300 r / min.

[0053] (3) The mixed powder was uniformly spread in a crucible, and was put into a tube furnace for heat treatment at 600 °C for 3 hours in a nitrogen atmosphere.

[0054] (4) After natural cooling to room temperature, the product was washed with deionized water for 3 times, and then was dried at 60 °C for 24 hours to obtain the fluorinated graphite.

[0055] Example 3

[0056] (1) 10 g of natural graphite powder (D50 particle size of 7.4 μm) and 2 g of NH4F (D50 particle size of 13.9 μm) were weighed.

[0057] (2) Put the graphite powder and NH4F into a ball mill tank, add an appropriate amount of stainless steel balls, the ball-to-material ratio is 15:1, ball mill in a ball mill for 18 hours, the ball mill rotation speed is 350 r / min.

[0058] (3) Uniformly spread the mixed powder in a crucible, put it into a muffle furnace, heat treat at 400 °C for 5 hours, the atmosphere is argon.

[0059] (4) After natural cooling to room temperature, wash with deionized water for 3 times, then dry at 70 °C for 16 hours, get the fluorinated graphite.

[0060] Example 4

[0061] (1) Weigh 10 g of artificial graphite powder (D50 particle size is 9.2 μm) and 4 g of KF (D50 particle size is 7.9 μm).

[0062] (2) Put the graphite powder and KF into a ball mill tank, add an appropriate amount of ceramic balls, the ball-to-material ratio is 20:1, ball mill in a ball mill for 30 hours, the ball mill rotation speed is 350 r / min.

[0063] (3) Uniformly spread the mixed powder in a crucible, put it into a tube furnace, heat treat at 700 °C for 2 hours, the atmosphere is nitrogen.

[0064] (4) After natural cooling to room temperature, wash with ethanol for 3 times, then dry at 90 °C for 10 hours, get the fluorinated graphite.

[0065] Example 5

[0066] (1) Weigh 10 g of natural graphite powder (D50 particle size is 5.1 μm) and 1 g of CaF2 (D50 particle size is 12.3 μm).

[0067] (2) Put the graphite powder and CaF2 into a ball mill tank, add an appropriate amount of stainless steel balls, the ball-to-material ratio is 20:1, ball mill in a ball mill for 10 hours, the ball mill rotation speed is 400 r / min.

[0068] (3) Uniformly spread the mixed powder in a crucible, put it into a muffle furnace, heat treat at 300 °C for 6 hours, the atmosphere is argon.

[0069] (4) After natural cooling to room temperature, wash with deionized water for 3 times, then dry at 60 °C for 20 hours, get the fluorinated graphite.

[0070] Example 6

[0071] (1) Weigh 10 g of artificial graphite powder (D50 particle size is 8.4 μm) and 5 g of NH4F (D50 particle size is 10.1 μm).

[0072] (2) Put the graphite powder and KF into a ball mill tank, add an appropriate amount of ceramic balls, the ball-to-material ratio is 20:1, ball mill in a ball mill for 20 hours, the ball mill speed is 400 r / min.

[0073] (3) Put the mixed powder evenly in a crucible, put it into a tube furnace, heat treat at 800 °C for 1 hour, the atmosphere is nitrogen.

[0074] (4) After natural cooling to room temperature, wash with ethanol 3 times, then dry at 80 °C for 12 hours, get the fluorinated graphite.

[0075] Example 7

[0076] (1) Take 10 g of natural graphite powder (D50 particle size is 8 pm) and 5 g of KF (D50 particle size is 14.7 pm).

[0077] (2) Put the graphite powder and KF into a container, mix them simply using a hand blender, make sure they are mixed evenly initially.

[0078] (3) Put the mixed powder evenly in a crucible, put it into a muffle furnace, heat treat at 500 °C for 4 hours, the atmosphere is argon.

[0079] (4) After natural cooling to room temperature, wash with deionized water 3 times, then dry at 80 °C for 12 hours, get the fluorinated graphite.

[0080] Example 8

[0081] (1) Take 10 g of natural graphite powder (D50 particle size is 8 pm) and 5 g of K2MnF6 (D50 particle size is 15.7 pm).

[0082] (2) Put the graphite powder and K2MnF6 into a ball mill tank, add an appropriate amount of stainless steel balls, the ball-to-material ratio is 15:1, ball mill in a ball mill for 24 hours, the ball mill speed is 300 r / min.

[0083] (3) Put the ball-milled powder evenly in a crucible, put it into a muffle furnace, heat treat at 500 °C for 4 hours, the atmosphere is argon.

[0084] (4) After natural cooling to room temperature, wash with deionized water 3 times, then dry at 80 °C for 12 hours, get the fluorinated graphite.

[0085] Comparative Example 1

[0086] (1) Take 10 g of natural graphite powder (D50 particle size is 8.5 pm), do not add any fluorine source.

[0087] (2) Put the graphite powder into a ball mill tank, add appropriate amount of stainless steel balls, the ball-to-material ratio is 15:1, ball mill in a ball mill for 24 hours, the rotation speed is 200 r / min.

[0088] (3) Uniformly spread the ball-milled powder in a crucible, put it into a muffle furnace, heat treat at 500°C for 4 hours, the atmosphere is argon.

[0089] (4) After natural cooling to room temperature, wash with deionized water for 3 times, then dry at 80°C for 12 hours, get the unfluorinated graphite.

[0090] Effect Implementation Example

[0091] Prepare the electrode using the graphite obtained in the above examples and comparative examples and assemble it into a battery, the preparation method of the battery is as follows:

[0092] 1. Preparation of negative electrode

[0093] (1) Material preparation

[0094] Conductive agent: Super P or acetylene black, 5-10 wt%.

[0095] Binder: polyvinylidene fluoride (PVDF), 5-10 wt%.

[0096] Solvent: N-methyl pyrrolidone (NMP).

[0097] (2) Mix the fluorinated graphite prepared in the above examples, conductive agent and binder according to the proportion, add appropriate amount of NMP, use a blender to stir at room temperature for 3-4 hours until a uniform slurry is formed. Use a doctor blade method to uniformly coat the slurry on a copper foil, the thickness is controlled at 80-100 μm. Dry at 60-80°C for 2-4 hours, then vacuum dry at 120-150°C for 12 hours. Use a roll press to press the dried electrode sheet, the pressure is 10-20 MPa, to improve the density and mechanical strength of the electrode. Cut the pressed electrode sheet into the required size, ready for use.

[0098] 2. Preparation of positive electrode

[0099] (1) Material preparation:

[0100] Lithium cobalt oxide (LiCoO2) or other commercial positive electrode materials.

[0101] Conductive agent: Super P or acetylene black, 5-10 wt%.

[0102] Binder: polyvinylidene fluoride (PVDF), 5-10 wt%.

[0103] Solvent: N-methyl pyrrolidone (NMP).

[0104] (2) Mix the positive active material, conductive agent and binder in proportion, add an appropriate amount of NMP, and stir at room temperature for 3-4 hours using a stirrer until a uniform slurry is formed. Use a doctor blade method to uniformly coat the slurry on an aluminum foil, with a thickness controlled at 80-100 pm. Dry at 60-80 °C for 2-4 hours, and then vacuum dry at 120-150 °C for 12 hours. The dried electrode sheet is pressed using a roll press machine at a pressure of 10-20 MPa to improve the density and mechanical strength of the electrode. The pressed electrode sheet is cut to the desired size for use.

[0105] 3. Battery assembly

[0106] Select a suitable separator, such as a polypropylene (PP) or polyethylene (PE) separator, a lithium ion battery electrolyte, and a battery case, such as a CR2032 button cell case. Place the positive electrode, separator, and negative electrode in the battery case in order, inject an appropriate amount of electrolyte, and seal the battery.

[0107] 4. Electrochemical performance test method

[0108] (1) Discharge capacity

[0109] Test conditions: Charge-discharge voltage range: 0.01-2.0 V (vs. Li / Li + ).

[0110] Current density: 0.1 C

[0111] Test temperature: 25 °C

[0112] Test procedure: Use a constant current charge-discharge device for charge-discharge testing. Record the discharge curve and calculate the discharge capacity.

[0113] (2) First coulombic efficiency (first efficiency)

[0114] Test conditions: Charge-discharge voltage range: 0.01-2.0 V (vs. Li / Li + ).

[0115] Current density: 0.1 C.

[0116] Test temperature: 25 °C.

[0117] Test procedure: Perform one complete charge-discharge cycle.

[0118] (3) 1000 cycle capacity retention rate

[0119] Test conditions: Charge-discharge voltage range: 0.01-2.0 V (vs. Li / Li + ).

[0120] Current density: 0.1 C.

[0121] Test temperature: 25°C.

[0122] Test procedure: Perform 1000 charge-discharge cycles and calculate the capacity retention rate at 1000 cycles.

[0123] (4) Rate performance

[0124] Test conditions: Charge-discharge voltage range: 0.01-2.0 V (vs. Li / Li + ).

[0125] Current density: 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C.

[0126] Test temperature: 25°C.

[0127] Test procedure: Perform charge-discharge tests at different current densities. Record the discharge capacity at different current densities.

[0128] (5) Direct current internal resistance (DCIR)

[0129] Test conditions: Charge-discharge voltage range: 0.01-2.0 V (vs. Li / Li + ).

[0130] Current density: 0.1 C.

[0131] Test temperature: 25°C.

[0132] Test procedure: Use a DC internal resistance tester to test. Apply a small current pulse (e.g. 10 mA) and record the voltage change.

[0133] (6) Electrochemical impedance spectroscopy (EIS)

[0134] Test conditions: Test frequency range: 1 MHz - 0.01 Hz.

[0135] AC perturbation amplitude: 10 mV.

[0136] Test temperature: 25°C.

[0137] Test procedure: Use an electrochemical workstation to perform EIS tests. Record the impedance spectrum. Analyze each impedance component in the impedance spectrum, such as ohmic resistance, charge transfer resistance and diffusion resistance.

[0138] 5. Standard test methods

[0139] Discharge capacity, initial efficiency, 1000 cycle capacity retention, rate capability: can refer to the International Electrotechnical Commission (IEC) standards, such as IEC 61960-3:2017 Portable Secondary Lithium Batteries and Battery Packs Part 3: Safety Requirements.

[0140] Direct current internal resistance (DCIR): can refer to the relevant test method in IEC 61960-3:2017.

[0141] Electrochemical impedance spectroscopy (EIS): can refer to ASTM E1065-17 Standard Guide for Electrochemical Impedance Spectroscopy Measurements.

[0142] The test results are shown in Tables 1 to 3.

[0143] Table 1 Capacity and initial efficiency test results of examples and comparative examples

[0144]

[0145] Table 2 Rate test results of examples and comparative examples

[0146]

[0147] Table 3 DCIR and EIS test results of examples and comparative examples

[0148]

[0149] It can be seen that the graphite negative electrode material prepared by solid phase fluorination method is significantly better than the unfluorinated graphite in terms of first coulombic efficiency, cycle stability and rate performance. This shows that the solid phase fluorination method is an effective and practical modification method for graphite negative electrode material, and has broad application prospects.

[0150] Fluorination treatment significantly improves the specific capacity of the graphite negative electrode material, and the discharge capacity of all examples at various rates is higher than that of the unfluorinated comparative example 1. This shows that fluorination treatment can effectively increase the lithium ion intercalation amount of the material and improve the lithium storage capacity of the material.

[0151] Fluorination treatment significantly improves the rate performance of the graphite negative electrode material, especially at high rates (2C and 5C), the discharge capacity of the examples is significantly higher than that of comparative example 1. This shows that fluorination treatment can improve the electrical conductivity and diffusion rate of lithium ions of the material, and improve the performance of the material under high rate charge and discharge conditions.

[0152] Fluorination treatment improves the first coulombic efficiency of the material and reduces the irreversible capacity loss, which is particularly evident at low rates (0.1C and 0.5C). This shows that fluorination treatment can improve the surface properties of the material, reduce side reactions, and improve the electrochemical stability of the material.

[0153] The fluorination treatment significantly reduces the internal resistance of the graphite negative electrode material, and the DCIR of all examples is lower than that of the non-fluorinated comparative example 1. This indicates that the fluorination treatment can effectively improve the conductivity of the material and reduce the energy loss inside the battery.

[0154] The fluorination treatment significantly reduces the charge transfer resistance and improves the electrochemical reaction activity of the material. The conductivity of the material is improved, and the solution resistance is reduced. The diffusion resistance of lithium ions in the material is reduced, and the diffusion rate of lithium ions is improved.

Claims

1. A method for producing a fluorine-doped graphite material, characterized by, It comprises the following steps: mixing graphite powder with fluorine source powder to obtain a preliminary material; the mass ratio of the graphite powder to the fluorine source powder is (2-10):1; the mixing is carried out by ball milling, the rotation speed of the ball milling is 300-400 r / min, the ball milling time is 10-25 h or 30 h, and the ball-to-material ratio of the ball milling is (15-20):1; the fluorine source powder is an inorganic fluorine source, and the inorganic fluorine source is KF, CaF2 or NH4F; heat treating the preliminary material at 300-800 °C to obtain a fluorine-doped graphite material; the fluorine-doped graphite material is a layered compound, and fluorine atoms are embedded between the layers of graphite.

2. The method for preparing fluorine-doped graphite material as described in claim 1, characterized in that, The rotation speed of the ball milling is 350 r / min. And / or, the ball milling time is 12 h, 18 h, 20 h or 24 h.

3. The method for preparing fluorine-doped graphite material as described in claim 1, characterized in that, The mass ratio of the graphite powder to the fluorine source powder is (2-3):

1.

4. The method of claim 1, wherein the fluorine-doped graphite material is prepared by the steps of: preparing a mixture of graphite and a fluorine compound; and heating the mixture at a temperature of 1,000°C or higher in an inert gas atmosphere. 5 The mass ratio of the graphite powder to the fluorine source powder is 2.5:1, 3.3:1 or 5:

1.

5. The method for preparing fluorine-doped graphite material as described in claim 1, characterized in that, The D50 particle size of the fluorine source powder is 5-20 μm.

6. The method of claim 5, wherein the fluorine-doped graphite material is prepared by the steps of: preparing a mixture of graphite and a fluorine compound; and heating the mixture at a temperature of 1,000°C or higher in an inert gas atmosphere. The D50 particle size of the fluorine source powder is 7.9 μm, 10.1 μm, 12 μm, 12.3 μm, 13.9 μm, 14.7 μm, 15.3 μm or 15.7 μm.

7. The method for preparing fluorine-doped graphite material as described in claim 1, characterized in that, The graphite powder meets one or more of the following conditions: ① The graphite powder is natural graphite powder or artificial graphite powder; ② The D50 particle size of the graphite powder is 5-20 μm; ③ The crystallinity of the graphite powder is greater than 95%; ④ The purity of the graphite powder is greater than 99.9%.

8. The method of claim 7, wherein the fluorine-doped graphite material is prepared by the steps of: preparing a mixture of graphite and a fluorine compound; and heating the mixture at a temperature of 1,000°C or higher in an inert gas atmosphere. 8 The graphite powder meets one or more of the following conditions: ① The D50 particle size of the graphite powder is 5.1 μm, 6.5 μm, 7.4 μm, 8 μm, 8.4 μm, 9.2 μm or 10.3 μm; ② The standard deviation of the particle size distribution of the graphite powder is less than 3 μm; ③ The crystallinity of the graphite powder is 96.3%.

9. The method for preparing fluorine-doped graphite material as described in claim 1, characterized in that, The heat treatment meets one or more of the following conditions: ① The temperature of the heat treatment is 500-700 °C or 800 °C; ② The time of the heat treatment is 1-10 h; ③ The heat treatment is carried out in an inert atmosphere.

10. The method of claim 9, wherein the fluorine-doped graphite material is prepared by the steps of: preparing a mixture of graphite and a fluorine compound; and heating the mixture at a temperature of 1,000°C or higher in an inert gas atmosphere. 10 The heat treatment meets one or more of the following conditions: ① The temperature of the heat treatment is 300 °C, 400 °C, 500 °C, 600 °C, 700 °C; ② The time of the heat treatment is 1 h, 2 h, 3 h, 4 h, 5 h and 6 h; ③ The inert atmosphere is argon or nitrogen.

11. The method of claim 1, wherein the fluorine-doped graphite material is prepared by the steps of: preparing a mixture of graphite and a fluorine compound; and heating the mixture to a temperature of 1000°C or higher in the presence of a reducing gas. 0 After the heat treatment, the process further comprises the steps of cooling, washing and drying.

12. The method for preparing fluorine-doped graphite material as described in claim 11, characterized in that, The preparation method of the fluorine-doped graphite material meets one or more of the following conditions: ① The cooling step comprises natural cooling to room temperature; ② The washing is carried out using deionized water or ethanol; ③ The drying temperature is 60-100 °C.

13. The method for preparing fluorine-doped graphite material as described in claim 12, characterized in that, The preparation method of the fluorine-doped graphite material meets one or more of the following conditions: ① The washing is carried out 2-5 times; ② The drying temperature is 60 °C, 70 °C, 80 °C or 90 °C; ③ The drying time is 10-25 h.

14. A fluorine-doped graphite material prepared by the preparation method of any one of claims 1-13.

15. Use of a fluorine-doped graphite material as claimed in claim 14 as a negative electrode material in a lithium-ion battery.

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