Graphite material, preparation method and application thereof, and lithium ion battery

Abstract

The invention discloses a graphite material, a preparation method and application thereof, and a lithium ion battery. The graphite material comprises a graphite matrix and a carbon coating layer, wherein the carbon coating layer coats the surface of the graphite matrix; the graphite matrix and the carbon coating layer both comprise graphite microcrystals; the graphite material meets the following conditions: a, 1.5 nm < = La < = 4.0 nm, 0.5 nm < = Lc < = 2.0 nm; b, 0.3 < = Csp3 / Csp2 < = 1.5; c, 0 lt; (ID / IG) L50 is less than or equal to 0.07. The preparation method of the graphite material comprises the following steps: S1, coating graphite with a coating agent to obtain a first precursor; wherein the coating agent contains a coating material and an assistant cross-linking agent; s2, performing pre-crosslinking on the first precursor to obtain a second precursor; and S3, graphitizing the second precursor to obtain the graphite material. After the obtained graphite material is applied to the lithium ion battery, the lithium ion battery has high capacity, excellent high-temperature performance and long-term cycle performance.

Description

Technical Field

[0001] The invention relates to a graphite material, a preparation method and application thereof, and a lithium ion battery. Background Art

[0002] With the increasingly serious environmental problems and the shortage of fossil energy, renewable clean energy has become the focus of social attention; among them, the wind power and photovoltaic industries are developing rapidly, but these electric energies are difficult to connect to the grid, so it is necessary to store excess electric energy. Among the many energy storage methods, lithium-ion batteries are the most feasible of the current energy storage solutions because of their long cycle life, high energy density and high industrial maturity. Graphite, because of its low lithium insertion potential and high lithium storage capacity, can be widely used as a negative electrode material for lithium-ion batteries. However, the existing energy storage application scenarios require lithium-ion batteries to have high energy density, high-temperature storage stability and long cycle life, which puts forward more comprehensive requirements on the performance of graphite.

[0003] Chinese patent application CN116356281A discloses a method and application for preparing a composite negative electrode material including an artificial SEI film. By atomic layer deposition, an artificial SEI interface layer is constructed on the graphite surface, the surface defects of the graphite are modified, and the stability and cycle performance of the graphite interface are improved. However, the cumbersome preparation process of the atomic layer deposition method and the high price of the equipment limit its industrial application; at the same time, the lithium aluminate used in the patent application has a certain solubility in polar solvents and has a certain risk of structural failure during long cycles. Using it as a coating layer cannot completely achieve the stability of the coating structure.

[0004] Surface non-graphitized carbon coating is a recognized method of graphite modification. Chinese patent application CN118136798A discloses a method for preparing medium-sulfur coke and its products. The patent reduces the interfacial side reactions during the first cycle by coating the surface of medium-sulfur coke with hard carbon, thereby improving the first cycle coulombic efficiency. However, there are still a large number of defect sites on the surface of hard carbon materials, and the high-temperature storage performance in lithium-ion batteries is still poor, making it difficult to achieve long-term stable cycling of lithium-ion batteries in extreme environments.

[0005] Surface modification strategy is another effective method for graphite modification. Lee et al. (Lee et al., Materials Letters 299 (2021) 130077) achieved surface functionalization modification by impregnating graphite with nitric acid solution. The surface functionalization modification strategy helps to form a structurally stable SEI film, which can significantly improve the cycle life and storage performance. However, the reversible capacity of the graphite negative electrode is low, and the reversible discharge capacity in the first week is only 275 mAh g -1 Moreover, the flammable and explosive properties of nitric acid add difficulty to the production process.

[0006] Therefore, a graphite modification strategy that combines high capacity, good high-temperature performance, and long-term cycling performance is urgently needed. Summary of the invention

[0007] In order to solve the technical defects of the existing graphite modification technology that it is difficult to balance high capacity, high temperature performance and long-term cycle performance, the present invention provides a graphite material and its preparation method and application, and a lithium-ion battery. After the graphite material is used in a lithium-ion battery, it has high capacity, excellent high temperature performance and long-term cycle performance.

[0008] To achieve the above purpose, the present invention adopts the following technical solution.

[0009] The present invention provides a graphite material, which comprises a graphite matrix and a carbon coating layer, wherein the carbon coating layer is coated on the surface of the graphite matrix; both the graphite matrix and the carbon coating layer comprise graphite microcrystals; and the graphite material satisfies the following conditions:

[0010] a. 1.5nm≤L a ≤4.0nm, 0.5nm≤L c ≤2.0nm;

[0011] Among them, the L a is the a-axis size of graphite crystallite, L c is the c-axis size of graphite crystallite;

[0012] b. 0.3 ≤ C sp3 / C sp2 ≤1.5;

[0013] Among them, the C sp3 The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The peak area of ​​the sp3 characteristic peak obtained in the spectrum, the C sp2 The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The peak area of ​​the sp2 characteristic peak obtained in the spectrum;

[0014] c、0<(I D / I G )L 50 ≤0.07;

[0015] Among them, the I D is the peak intensity of the D peak obtained in the Raman scan spectrum of the graphite material, and the I G is the peak intensity of the G peak obtained in the Raman scanning spectrum of the graphite material, and the L 50 For I D / I G Median of the cumulative distribution.

[0016] In the present invention, the L a , L c It can reflect the crystallinity of the graphite material and can be obtained after processing and calculating the XRD test results; specifically:

[0017] The half-peak widths of the diffraction peaks corresponding to the (002) and (110) crystal planes were measured by XRD, and then substituted into the Scherrer formula to calculate L a and L c ;

[0018] ;

[0019] Where K is a constant; λ is the wavelength of X-rays; β is the half-width of the diffraction peak; θ is the diffraction angle; the value of the constant K is related to the definition of β. When β is 110° half-width of the diffraction peak, K is 0.89, and the D value at this time is L a ; When β is the half width height of the diffraction peak of 002, K is 1.84, and the D value at this time is L c .

[0020] In the present invention, the C sp3 / C sp2 It can reflect the sp3 carbon hybridization degree on the surface of the graphite material.

[0021] In the present invention, the (I D / I G )L 50 It can reflect the surface defect degree of the graphite material.

[0022] In some embodiments, the graphite material satisfies one or more of the following conditions:

[0023] a. 2.0nm≤L a ≤3.0nm、0.7nm≤L c ≤1.5nm; said L a For example, it is 2.28nm, 2.31nm, 2.32nm, 2.33nm or 2.35nm; c For example, 0.72nm, 0.76nm, 0.77nm, 0.78nm or 0.80nm;

[0024] b. 0.5 ≤ C sp3 / C sp2 ≤1.5, preferably 0.6≤C sp3 / C sp2 ≤0.8; C sp3 / C sp2 For example, 0.61;

[0025] c、0<(I D / IG )L 50 ≤0.06; said (I D / I G )L 50 For example, 0.051, 0.054, 0.055, 0.057 or 0.058.

[0026] In some embodiments, the graphite material further satisfies the following conditions:

[0027] 0.04≤C C=O / C C1s ≤0.2; preferably 0.06≤C C=O / C C1s ≤0.2, more preferably 0.07≤C C=O / C C1s ≤0.15, C C=O / C C1s For example, 0.08, 0.09 or 0.10;

[0028] Among them, the C C=O The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The C C=O The peak area of ​​the characteristic peak, the C C1s The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The C 1s The total peak area of ​​the characteristic peaks.

[0029] In some embodiments, the graphite material further satisfies one or more of the following conditions:

[0030] a. Specific surface area: 0.9-3m 2 / g;

[0031] b. Particle size D50 is 5-20 μm;

[0032] c. Tap density is 1.0-1.5g / cm 3 ;

[0033] d. The degree of graphitization is above 93%.

[0034] In the present invention, the graphitization degree may refer to the degree to which the crystal structure of the carbon material is close to the ideal graphite crystal; the interlayer spacing d of the (002) crystal plane may be determined by XRD. 002 , and substitute it into the following Mering–Maire formula to calculate (G is the degree of graphitization):

[0035] .

[0036] The present invention also provides a method for preparing a graphite material, which comprises the following steps:

[0037] S1, coating graphite with a coating agent to obtain a first precursor;

[0038] Wherein, the coating agent contains a coating material and a cross-linking agent;

[0039] S2, pre-crosslinking the first precursor to obtain a second precursor;

[0040] S3. Graphitizing the second precursor to obtain the graphite material.

[0041] The present invention adopts the steps of coating, pre-crosslinking and graphitization to modify the graphite, and at the same time adjusts the graphite crystallite size, surface sp3 hybridization degree and surface defect degree in the graphite material; wherein the auxiliary crosslinking agent in step S1 can further increase the crosslinking degree of the coating layer in the pre-crosslinking step of step S2, and further improve the surface sp3 carbon hybridization degree when the graphitization treatment is performed in step S3.

[0042] In some embodiments, in step S1, the graphite includes artificial graphite and / or natural graphite. The graphite may refer to graphite obtained after pretreatment, such as graphite obtained by crushing, grinding and classification.

[0043] In some embodiments, in step S1, the coating material includes a water-soluble modified resin, preferably one or more of a water-soluble phenolic resin, a water-based polyurethane resin, a water-based acrylic resin, a water-based alkyd resin and a urea-formaldehyde resin.

[0044] In the present invention, by selecting a coating material having a certain degree of crosslinking and containing one or more of hydroxyl, aldehyde and carboxyl groups, the content of carbon-oxygen double bonds on the surface of the obtained graphite material can be further improved, thereby enhancing the stability of the SEI film formed during use.

[0045] In some embodiments, in step S1, the auxiliary cross-linking agent includes one or more of caffeic acid, benzoic acid peroxide, terephthalaldehyde, terephthalic acid and phosphoric acid.

[0046] In some embodiments, in step S1, the mass ratio of the coating agent to the auxiliary cross-linking agent is 100:(1-10), for example, 100:8.

[0047] In some embodiments, in step S1, the mass ratio of the graphite to the coating agent is 100:(0.1-45), for example, 100:1.5, 100:2 or 100:2.5.

[0048] In some embodiments, in step S1, the coating temperature is 100-150°C, for example, 120°C.

[0049] In some embodiments, in step S1, the coating time is 0.1-2 hours, for example, 15 minutes.

[0050] In some embodiments, in step S1, the coating is performed under stirring; the stirring speed is preferably 130-220 rpm, such as 200 rpm.

[0051] In some embodiments, in step S2, the pre-crosslinking temperature is 400-500°C, for example 450°C.

[0052] In some embodiments, in step S2, the pre-crosslinking time is 0.5-3 h, for example 2 h.

[0053] In some embodiments, in step S3, the graphitization temperature is 2500-3000°C, for example, 2900°C.

[0054] In some embodiments, in step S3, the graphitization time is 40-50 hours, for example 48 hours.

[0055] In some embodiments, in step S3, the graphitization further includes the steps of demagnetization and screening.

[0056] The present invention also provides a graphite material, which is prepared by the preparation method as described above.

[0057] In some embodiments, the graphite material is as described above.

[0058] The present invention also provides a use of the graphite material as described above in an electrochemical device.

[0059] In some embodiments, the electrochemical device includes, but is not limited to, a laptop computer, a mobile computer, an electronic book player, a portable phone, a portable printer, a portable fax machine, a headset, a video recorder, a television, a handheld vacuum cleaner, a portable CD, and an electronic notebook.

[0060] The present invention also provides a lithium ion battery, which comprises the graphite material as described above.

[0061] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0062] The reagents and raw materials used in the present invention are commercially available.

[0063] The positive and progressive effects of the present invention are:

[0064] The present invention modifies graphite by coating, pre-crosslinking and graphitization to obtain a graphite material that meets certain structural parameters; the obtained graphite material has a higher bulk crystallinity (i.e., crystallite size) and a coating layer with higher chemical stability; after being further used in lithium-ion batteries, it can have high capacity while significantly improving its high-temperature performance and long-term cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a scanning electron microscope (SEM) image of the graphite material of Example 1 of the present invention.

[0066] Figure 2 This is the X-ray photoelectron spectrum C1s diagram of the graphite material of Example 1 of the present invention.

[0067] Figure 3 This is the infrared spectrum of the graphite material of Example 1 of the present invention.

[0068] Figure 4 This is a Raman scan of the graphite material of Example 1 of the present invention.

[0069] Figure 5 This is a Raman scan of the graphite material of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0070] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0071] In the following examples and comparative examples, raw materials are all common commercially available products unless otherwise specified and can be purchased from the market.

[0072] Example 1

[0073] The graphite material of this embodiment is prepared according to the following steps:

[0074] 1. The artificial graphite is crushed, ground and classified to obtain graphite raw material, and its particle size D50 is 5μm-20μm;

[0075] 2. The graphite raw material obtained in step 1 and the coating agent (coating material - water-soluble phenolic resin, cross-linking agent - caffeic acid; the mass ratio of the two is 100:8) are mixed for coating; wherein the mass ratio of the graphite raw material to the coating agent is 100:1.5; the coating conditions are: rotation speed of 200 rpm, time of 15 min, temperature of 120 ° C; the first precursor is obtained after the material is discharged;

[0076] 3. The first precursor obtained in step 2 is pre-crosslinked at 450° C. for 2 hours, and the second precursor is obtained after the material is discharged;

[0077] 4. The pre-crosslinked precursor obtained in step 3 is graphitized at 2900° C. for 48 hours; the graphite material is obtained after mixing, demagnetization and screening.

[0078] Example 2

[0079] The difference from Example 1 is that in step 2, the mass ratio of the graphite raw material and the coating agent is adjusted to 100:2.

[0080] The rest is the same as in Example 1 and will not be described again here.

[0081] Example 3

[0082] The difference from Example 1 is that in step 2, the mass ratio of the graphite raw material and the coating agent is adjusted to 100:2.5.

[0083] The rest is the same as in Example 1 and will not be described again here.

[0084] Example 4

[0085] The difference from Example 1 is that in step 2, the coating material is adjusted to a water-soluble polyurethane resin, and the auxiliary cross-linking agent is adjusted to phosphoric acid.

[0086] The rest is the same as in Example 1 and will not be described again here.

[0087] Example 5

[0088] The difference from Example 1 is that in step 2, the coating material is adjusted to a water-soluble polyacrylic acid resin, and the auxiliary cross-linking agent is adjusted to terephthalaldehyde.

[0089] The rest is the same as in Example 1 and will not be described again here.

[0090] Example 6

[0091] The difference from Example 1 is that in step 2, the coating material is adjusted to a water-soluble alkyd resin, and the auxiliary cross-linking agent is adjusted to terephthalic acid.

[0092] The rest is the same as in Example 1 and will not be described again here.

[0093] Comparative Example 1

[0094] 1. Select artificial graphite for crushing, grinding and grading to obtain graphite raw material, whose D50 is 5μm-20μm;

[0095] 2. The graphite raw material obtained in step 1 is graphitized at 2900° C. for 48 hours to obtain a graphitized product;

[0096] 3. The graphitized product in step 2 and the coating agent (containing only the coating material - water-soluble phenolic resin) are mixed and coated; wherein the mass ratio of the graphite raw material to the coating agent is 100:1.5; the coating conditions are: the rotation speed is 200 rpm, the time is 15 min, the temperature is 120 ° C, and the coated product is obtained after the material is discharged;

[0097] 4. The coated product obtained in step 3 is carbonized at 1150° C., and the graphite material of this comparative example is obtained after the material is discharged.

[0098] Comparative Example 2

[0099] 1. Select artificial graphite for crushing, grinding and grading to obtain graphite raw material, whose D50 is 5μm-20μm;

[0100] 2. The graphite raw material obtained in step 1 and the coating agent (containing only the coating material - water-soluble phenolic resin) are mixed and coated; wherein the mass ratio of the graphite raw material to the coating agent is 100:1.5; the coating conditions are: rotation speed of 200 rpm, time of 15 min, temperature of 120°C; the precursor is obtained after the material is discharged;

[0101] 3. The precursor obtained in step 2 is graphitized at 2900° C. for 48 hours; the graphite material of this comparative example is obtained after mixing, demagnetization and screening.

[0102] Effect Example 1 Physical and Chemical Parameters Test

[0103] The graphite materials of Examples 1-6 and Comparative Examples 1-2 were tested as follows:

[0104] 1. X-ray photoelectron spectroscopy test (C sp3 / C sp2 , C C=O / C C1s Determination of ):

[0105] The test was carried out using an X-ray photoelectron spectrometer (XPS, instrument model: Shimadzu Axis Supra+): the target material was monochromated Al, the full spectrum test step size was 1 eV, the scanning time was 120 s, and the resolution was 160; the high-resolution narrow spectrum test step size was 0.1 eV, the scanning time was 60 s, and the resolution was 40.

[0106] (1) X-ray photoelectron spectroscopy C 1s The peak area of ​​the sp3 characteristic peak obtained in the spectrum can be recorded as C sp3 , by X-ray photoelectron spectroscopy C 1s The peak area of ​​the sp2 characteristic peak obtained in the spectrum can be recorded as C sp2 Calculate the ratio of the two to get Csp3 / C sp2 .

[0107] (2) X-ray photoelectron spectroscopy C 1s The C C=O The peak area of ​​the characteristic peak can be recorded as C C=O , by X-ray photoelectron spectroscopy C 1s The C 1s The total peak area of ​​the characteristic peak can be recorded as C sp2 Calculate the ratio of the two to get C C=O / C C1s .

[0108] 2. X-ray diffraction test (L a , L c And determination of graphitization degree):

[0109] The test was carried out using an X-ray diffractometer (XRD, instrument model: Bruker D8 ADVANCE): the target material was Cu Kα, the voltage and current were 40 KV / 40 mA, the scanning angle range was 5-80°, the scanning step length was 0.00836°, and the step time was 0.3 s.

[0110] (1) The half-peak widths of the diffraction peaks corresponding to the (002) and (110) crystal planes were measured by XRD, and then substituted into the Scherrer formula to calculate L a and L c ;

[0111] ;

[0112] Where K is a constant; λ is the wavelength of X-rays; β is the half-width of the diffraction peak; θ is the diffraction angle; the value of the constant K is related to the definition of β. When β is 110° half-width of the diffraction peak, K is 0.89, and the D value at this time is L a ; When β is the half width height of the diffraction peak of 002, K is 1.84, and the D value at this time is L c .

[0113] (2) Determination of the interlayer spacing d of the (002) crystal plane by XRD 002 , and substitute it into the following Mering–Maire formula to calculate the degree of graphitization, denoted as G:

[0114] .

[0115] 3. Infrared spectrum test:

[0116] The infrared spectrum test was carried out using a total reflection Fourier transform infrared spectrometer (ATR-FTIR, instrument model: Thermo Fisher PerkinElmer Spectrum 100), with reference to the national standard GB / T 21186-2007 "Fourier transform infrared spectrometer", and the infrared spectrum test was carried out using the ATR total reflection method.

[0117] 4. Raman spectroscopy test (I D / I G )L 50 Determination of ):

[0118] Raman spectrometer (instrument model: Renishaw inVia) was used for testing: laser wavelength 532nm, test range 500-2000cm -1 .

[0119] Measure the peak intensities of D peak and G peak respectively, and take I D / I G The median of the cumulative distribution L 50 That's it.

[0120] 5. Specific surface area test:

[0121] In accordance with the national standard “Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method” (GB / T 19587-2017), the test was carried out using a specific surface area analyzer (model: TriStar Ⅱ 3020 Plus) using the nitrogen adsorption method.

[0122] 6. Particle size analysis test:

[0123] The particle size analysis was performed using a Malvern particle size analyzer (model: MasterSizer 2000). 20 mg of graphite material was added to a 50 ml crystallization beaker, and 20 ml of ethanol was added. The sample dispersion was completely dispersed in the ethanol in a 200 W ultrasonic cleaner for 30 minutes. The sample dispersion was obtained. The dispersion was tested using a Malvern particle size analyzer to obtain the particle size D50 of the graphite material.

[0124] 7. Tap density TD test:

[0125] In accordance with the national standard GB / T 24533-2019, a density analyzer (model GeoPyc 1365) was used for testing.

[0126] After testing, the graphite materials obtained in Examples 1-6 all meet the following parameters:

[0127] (1) Specific surface area is 0.9-3m 2 / g;

[0128] (2) Particle size D50 is 5-20 μm;

[0129] (3) Tap density is 1.0-1.5g / cm 3 ;

[0130] (4) The degree of graphitization is above 93%.

[0131] The specific parameters are shown in Table 1 and Figure 1-Figure 5 shown.

[0132] Table 1

[0133]

[0134] in, Figure 1 This is a scanning electron microscope (SEM) image of the graphite material of Example 1 of the present invention; Figure 2 This is a C1s graph of the X-ray photoelectron spectrum of the graphite material of Example 1 of the present invention; Figure 3 This is an infrared spectrum of the graphite material of Example 1 of the present invention; Figure 4 This is a Raman scan of the graphite material of Example 1 of the present invention; Figure 5 This is a Raman scan of the graphite material of comparative example 1 of the present invention. Combined with the above results, it is shown that the surface of the graphite material of the embodiment of the present invention can maintain a certain sp3 hybridization degree and carbon-oxygen double bond content, has a lower surface defect degree, and has a higher overall crystallite size.

[0135] Effect Example 2 Electrochemical Performance Test

[0136] The graphite materials of Examples 1-6 and Comparative Examples 1-2 were made into corresponding pole pieces and lithium-ion batteries according to the following test methods, and the following tests were performed:

[0137] (1) Preparation of pole pieces: The graphite material, conductive agent (Super P), dispersant (CMC) and binder (SBR) of Examples 1-6 and Comparative Examples 1-2 were mixed in a mass ratio of 95.5:1.5:1.5:1.5 to prepare a slurry, stirred and mixed, and then coated on a copper foil current collector. After drying at room temperature, the slurry was placed in a vacuum oven and further dried at 60°C for 12 h to obtain a pole piece.

[0138] (2) Battery assembly: The above-obtained electrodes were cut into circular electrodes with a diameter of 10 mm and an active material loading of 1.3 mg / cm 2; Metal lithium sheet was used as the counter electrode; 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, with 5% volume of fluoroethylene carbonate added) was used as the electrolyte; a polypropylene microporous diaphragm was used; 2032-type button cells were assembled in an argon atmosphere glove box, and 50 μL of electrolyte was added to each battery.

[0139] (3) Performance test: The prepared button battery was subjected to electrical performance test using a blue electric tester CT3002A. The charge and discharge cut-off voltages were 2.0 V and 0.005 V, respectively. The battery was then activated at a rate of 0.05 C and charged and discharged at a rate of 0.2 C. The first charge capacity, first cycle coulombic efficiency and 100 cycle capacity retention rate (%) of the battery were obtained at 25°C. The capacity retention rate (%) was measured after high-temperature storage at 60°C for 7 days.

[0140] The results are shown in Table 2.

[0141] Table 2

[0142]

[0143] As can be seen from the above results, the lithium-ion batteries prepared from the graphite materials of Examples 1-6 of the present invention have a capacity of not less than 350 mAh / g, an initial efficiency of not less than 94%, a capacity retention rate of not less than 79% after 7 days of high-temperature storage at 60°C, and a capacity retention rate of not less than 92% after 100 cycles at 25°C; while the parameters of Comparative Examples 1-2, except for the capacity, are significantly reduced. This shows that when the graphite materials of Examples 1-6 of the present invention are used in lithium-ion batteries, high capacity can be ensured while significantly improving their initial efficiency, high-temperature performance, and long-term cycle performance.

Claims

1. A graphite material, characterized in that: The graphite material comprises a graphite matrix and a carbon coating layer, wherein the carbon coating layer is coated on the surface of the graphite matrix; both the graphite matrix and the carbon coating layer comprise graphite crystallites; and the graphite material satisfies the following conditions: a、1.5nm≤L a ≤4.0nm,0.5nm≤L c ≤2.0nm; Among them, the L a is the a-axis size of graphite crystallite, L c is the c-axis size of graphite crystallite; b、0.3≤C sp3 / C sp2 ≤1.5; Among them, the C sp3 The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The peak area of ​​the sp3 characteristic peak obtained in the spectrum, the C sp2 The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The peak area of ​​the sp2 characteristic peak obtained in the spectrum; c、0<(I D / I G )L 50 ≤0.07; Among them, the I D is the peak intensity of the D peak obtained in the Raman scan spectrum of the graphite material, and the I G is the peak intensity of the G peak obtained in the Raman scanning spectrum of the graphite material, and the L 50 For I D / I G Median of the cumulative distribution.

2. The graphite material according to claim 1, characterized in that The graphite material meets one or more of the following conditions: a、2.0nm≤L a ≤3.0nm、0.7nm≤L c ≤1.5nm; said L a For example, it is 2.28nm, 2.31nm, 2.32nm, 2.33nm or 2.35nm; c For example, 0.72nm, 0.76nm, 0.77nm, 0.78nm or 0.80nm; b. 0.5≤C sp3 / C sp2 ≤1.5, preferably 0.6≤C sp3 / C sp2 ≤0.8; C sp3 / C sp2 For example, 0.61; c、0<(I D / I G )L 50 ≤0.06; said (I D / I G )L 50 For example, 0.051, 0.054, 0.055, 0.057 or 0.

058.

3. The graphite material according to claim 1, characterized in that The graphite material meets the following conditions: 0.04≤C C=O / C C1s ≤0.2, preferably 0.06≤C C=O / C C1s ≤0.2, more preferably 0.07≤C C=O / C C1s ≤0.15, C C=O / C C1s For example, 0.08, 0.09 or 0.10; Among them, the C C=O The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The C C=O The peak area of ​​the characteristic peak, the C C1s The graphite material is subjected to X-ray photoelectron spectroscopy C 1s The C 1s The total peak area of ​​the characteristic peaks.

4. The graphite material according to claim 1, characterized in that The graphite material meets one or more of the following conditions: a. Specific surface area: 0.9-3m 2 / g; b. Particle size D50 is 5-20 μm; c. Tap density is 1.0-1.5g / cm 3 ; d. The degree of graphitization is above 93%.

5. A method for preparing a graphite material, characterized in that: The preparation method of the graphite material comprises the following steps: S1, coating graphite with a coating agent to obtain a first precursor; Wherein, the coating agent contains a coating material and a cross-linking agent; S2, pre-crosslinking the first precursor to obtain a second precursor; S3. Graphitizing the second precursor to obtain the graphite material.

6. The method for preparing the graphite material according to claim 5, characterized in that: The method for preparing the graphite material satisfies one or more of the following conditions: a. In step S1, the graphite includes artificial graphite and / or natural graphite; b. In step S1, the coating material includes a water-soluble modified resin, preferably one or more of a water-soluble phenolic resin, a water-based polyurethane resin, a water-based acrylic resin, a water-based alkyd resin and a urea-formaldehyde resin; c. In step S1, the auxiliary cross-linking agent includes one or more of caffeic acid, benzoic acid peroxide, terephthalaldehyde, terephthalic acid and phosphoric acid; d. In step S1, the mass ratio of the coating material to the auxiliary cross-linking agent is 100:(1-10), for example, 100:8; e. In step S1, the mass ratio of the graphite to the coating agent is 100:(0.1-45), for example, 100:1.5, 100:2 or 100:2.5; f. In step S1, the coating temperature is 100-150°C, for example, 120°C; g. In step S1, the coating time is 0.1-2h, for example 15min; h. In step S1, the coating is carried out under stirring; the stirring speed is preferably 130-220 rpm, for example 200 rpm.

7. The method for preparing the graphite material according to claim 5, characterized in that: The method for preparing the graphite material satisfies one or more of the following conditions: a. In step S2, the pre-crosslinking temperature is 400-500°C, for example 450°C; b. In step S2, the pre-crosslinking time is 0.5-3h, for example 2h; c. In step S3, the graphitization temperature is 2500-3000° C., for example, 2900° C.; d. In step S3, the graphitization time is 40-50 hours, for example 48 hours; e. In step S3, the graphitization further includes the steps of demagnetization and screening.

8. A graphite material, characterized in that: The graphite material is prepared by the method for preparing the graphite material according to any one of claims 5 to 7.

9. Use of the graphite material according to any one of claims 1 to 4 and 8 in an electrochemical device.

10. A lithium ion battery, characterized in that: The lithium ion battery comprises the graphite material according to any one of claims 1 to 4 and 8.

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