Preparation method of artificial graphite negative electrode material

Abstract

The invention relates to the field of negative electrode materials, in particular to a preparation method of an artificial graphite negative electrode material, which comprises the following steps: preparation of a boron nitride precursor: mixing boric acid and a nitrogen source and then adding into a solvent to form a complex; and heating the complex to evaporate the solvent to obtain the boron nitride precursor, first coating: mixing graphitized coke with the boron nitride precursor according to a mass ratio of 100: (1-10) to obtain a first mixture; calcining the first mixture to obtain a first coated product; second coating: mixing the first coating product with a carbon source according to a mass ratio of 100: (0.5-10) to obtain a second mixture; and calcining the second mixture to obtain a second coated product. The negative electrode material prepared by the embodiment of the invention can improve the first efficiency, the high-temperature storage function and the cycle life of the battery.

Description

Technical Field

[0001] This application relates to the field of anode materials, specifically to a method for preparing an artificial graphite anode material. Background Technology

[0002] Graphite anode materials are widely used in lithium-ion batteries due to their excellent conductivity, high theoretical specific capacity, and good cycle stability. However, the intercalation of solvated lithium ions and the co-intercalation of solvent molecules can easily cause delamination between layers in graphite materials. The organic electrolyte continuously reduces and decomposes on the newly formed surface, generating a new solid electrolyte interphase (SEI) film. This process consumes a large number of lithium ions, reducing the battery's initial efficiency and cycle life.

[0003] In related technologies, graphite materials are usually modified by coating with different types of carbon and metal elements. However, this method can only solve one of the material's capacity or performance, and the improvement of overall performance is not significant, thus limiting its application scope. Summary of the Invention

[0004] The present invention solves at least one of the problems of the related art in the following aspects.

[0005] The first aspect of this application provides a method for preparing an artificial graphite anode material, comprising: preparing a boron nitride precursor, comprising: mixing boric acid with a nitrogen source and adding it to a solvent to form a complex; and heating the complex to evaporate the solvent to obtain the boron nitride precursor, wherein the nitrogen source is selected from one or more of urea, melamine, and dicyandiamide; a first coating, comprising: mixing graphitized coke with the boron nitride precursor at a mass ratio of 100:(1-10) to obtain a first mixture; and calcining the first mixture to obtain a first coated product; and a second coating, comprising: mixing the first coated product with a carbon source at a mass ratio of 100:(0.5-10) to obtain a second mixture; and calcining the second mixture to obtain a second coated product.

[0006] In this embodiment, a boron nitride precursor is used to perform a first coating on the surface of graphitized coke, forming a layered coating layer that is uniform and covers a large area. Furthermore, a carbon source is used to perform a second coating on the surface of the first coated product, resulting in an artificial graphite anode material with excellent overall performance. The anode material prepared in this embodiment can simultaneously improve the battery's initial efficiency, high-temperature storage capacity, and cycle life.

[0007] Compared to coating the surface of artificial graphite material with a mixture of boron nitride and carbon source in one step, the embodiments of this application use a two-step coating process to sequentially coat the boron nitride precursor and the carbon source, thereby comprehensively improving the first efficiency, room temperature capacity retention, and high temperature capacity retention of the artificial graphite anode material.

[0008] This application uses specific amounts of boron nitride precursor and nitrogen source for coating; excessive or insufficient amounts will affect the electrochemical performance of the resulting artificial graphite anode material. For example, a high amount of boron nitride will reduce the capacity of the resulting artificial graphite anode material, while insufficient amounts will fail to achieve the goal of comprehensively improving the electrochemical performance of the resulting artificial graphite anode material.

[0009] In some embodiments, the solvent is selected from one or more of ethylene glycol, glycerol, N,N-dimethylformamide (DMF), and acetic acid.

[0010] In some embodiments, the boric acid is mixed with the nitrogen source at a mass ratio of 3:(1-15).

[0011] In some embodiments, the boric acid is mixed with the nitrogen source at a mass ratio of 2:(1-4).

[0012] In some embodiments, the molar ratio of boric acid to the solvent is 1:(10-20).

[0013] In some embodiments, the preparation of the boron nitride precursor includes: heating the complex at 100-150°C to evaporate the solvent, thereby obtaining the boron nitride precursor.

[0014] In some embodiments, the preparation of the boron nitride precursor includes: heating the complex at 120-140°C to evaporate the solvent, thereby obtaining the boron nitride precursor.

[0015] In some embodiments, the coke is selected from one or more of needle coke, raw petroleum coke, calcined petroleum coke, and pitch coke.

[0016] In some embodiments, the graphitization includes: a first calcination and a second calcination, wherein the first calcination includes holding the raw material at 800-1000°C for 8-12 hours, and wherein the second calcination includes holding the raw material after the first calcination at 2800-3000°C for 0.5-1.5 hours.

[0017] In some embodiments, the graphitization includes: pretreatment, a first calcination, and a second calcination, wherein the pretreatment includes one or more of crushing, drying, grinding, and shaping to obtain a raw material to be calcined, wherein the particle size Dv of the raw material to be calcined is... 50 It is 6-16μm.

[0018] In some embodiments, the particle size Dv of the graphitized coke 50 The micrometer diameter is 5-15 μm, and the tap density is 1.0-1.3 g / cm³. 3 .

[0019] In some embodiments, the carbon source is selected from one or more of asphalt, starch, glucose, phenolic resin, and epoxy resin.

[0020] In some embodiments, the first coating comprises: mixing graphitized coke with the boron nitride precursor at a mass ratio of 100:(2-5) to obtain a first mixture.

[0021] In some embodiments, the first coating includes calcining a first mixture at 800-1500°C to obtain a first coated product.

[0022] In some embodiments, the first coating includes calcining a first mixture at 800-1500°C for 2-8 hours to obtain a first coated product.

[0023] In some embodiments, the first coating includes calcining a first mixture at 1000-1400°C to obtain a first coated product.

[0024] In some embodiments, the first coating includes calcining a first mixture at 1000-1400°C for 2-8 hours to obtain a first coated product.

[0025] In some embodiments, the heating rate during calcination in the first coating is 2-8 °C / min.

[0026] In some embodiments, the heating rate during calcination in the second coating is 2-8 °C / min.

[0027] In some embodiments, the second coating includes: mixing the first coating product with a carbon source at a mass ratio of 100:(1-5) to obtain a second mixture.

[0028] In some embodiments, the second coating includes calcining the second mixture at 900-1400°C to obtain the second coated product.

[0029] Compared with related technologies, the embodiments of this application achieve at least the following beneficial effects:

[0030] This application embodiment uses boron nitride nanosheets and a carbon source to double-coat graphite. The boron nitride precursor prepared in this application embodiment has ion-conducting properties. After being coated onto the graphite material, it reduces the contact between organic matter in the electrolyte and graphite without hindering lithium ions from intercalating into the graphite through the boron nitride precursor, thus reducing the formation of the SEI film and improving the first-stage efficiency. In addition, the boron nitride precursor prepared in this application embodiment has good high-temperature resistance and exhibits inertness to lithium ions, resulting in no lithium consumption at high temperatures and less initial SEI film formation. Therefore, the SEI film rupture of this anode material is relatively less likely to occur at high temperatures or during long-term use. The combined effect of these two factors results in batteries made using this artificial graphite anode material having better high-temperature storage performance and cycle life. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to specific embodiments. The embodiments given are merely illustrative of the invention and are not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0032] This application provides a method for preparing an artificial graphite anode material, including steps S100-S300.

[0033] Step S100: Preparation of boron nitride precursor, comprising: mixing boric acid with a nitrogen source and adding it to a solvent to form a complex; and heating the complex to evaporate the solvent to obtain the boron nitride precursor, wherein the nitrogen source is selected from one or more of urea, melamine and dicyandiamide.

[0034] Compared to hexagonal boron nitride, rhombohedral boron nitride (RBN), cubic boron nitride (CBN), and wurtzite boron nitride (WBN) in related technologies, the boron nitride precursor prepared in this application provides advantages such as a uniform coating layer and a larger coating area when used to coat graphitized coke. In this application, the boron nitride coating layer produced by sintering the boron nitride precursor is lamellar, which can uniformly coat graphite during the sintering process. Compared to commercially available stable boron nitride, the boron nitride precursor prepared in this application is easier to coat the graphite surface.

[0035] Compared to coating the surface of artificial graphite material with a mixture of boron nitride and carbon source in one step, the embodiments of this application use a two-step coating process to sequentially coat the boron nitride precursor and the carbon source, thereby comprehensively improving the first efficiency, room temperature capacity retention, and high temperature capacity retention of the artificial graphite anode material.

[0036] This application uses specific amounts of boron nitride precursor and nitrogen source for coating; excessive or insufficient amounts will affect the electrochemical performance of the resulting artificial graphite anode material. For example, a high amount of boron nitride will reduce the capacity of the resulting artificial graphite anode material, while insufficient amounts will fail to achieve the goal of comprehensively improving the electrochemical performance of the resulting artificial graphite anode material.

[0037] In step S100, the mixing ratio of boric acid to the nitrogen source is 3:(1-15) (e.g., 3:2, 3:3, 3:4, 3:5, 3:6, 3:7, 3:8, 3:9, 3:10, 3:11, 3:12, 3:13, 3:14).

[0038] In some embodiments, the mixing ratio of boric acid to the nitrogen source is 2:(1-4) (e.g., 2:2, 2:3).

[0039] In step S100, the molar ratio of boric acid to solvent is 1:(10-20) (e.g., 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19).

[0040] In step S100, the boron nitride precursor is obtained by heating the complex at 100-150°C (e.g., 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C) to evaporate the solvent.

[0041] In some embodiments, the boron nitride precursor is obtained by heating the complex at 120-140°C (e.g., 125°C, 130°C, 135°C, 140°C) to evaporate the solvent.

[0042] Step S200: First coating, comprising: mixing graphitized coke with the boron nitride precursor at a mass ratio of 100:(1-10) (e.g., 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9) to obtain a first mixture; and calcining the first mixture to obtain a first coated product.

[0043] The coating method provided in this application is applicable to various graphite materials, including but not limited to graphitized needle coke, raw petroleum coke, calcined petroleum coke, and pitch coke. In some embodiments, the graphitization includes: pretreatment, a first calcination, and a second calcination, wherein the pretreatment includes one or more of crushing, drying, grinding, and shaping to obtain the raw material to be calcined, wherein the particle size Dv of the raw material to be calcined is... 50The particle size is 6-16 μm (e.g., 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm). In some embodiments, the particle size Dv of the graphitized coke is... 50 The micrometer size is 5-15 μm (e.g., 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm), and the tap density is 1.0-1.3 g / cm³. 3 (e.g., 1.1 g / cm³) 3 1.2g / cm 3 In some embodiments, the graphitization includes: a first calcination and a second calcination, wherein the first calcination includes holding the raw material at 800-100°C (e.g., 850°C, 900°C, 950°C) for 8-12 hours (e.g., 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours), and wherein the second calcination includes holding the raw material that has undergone the first calcination at 2800°C for 0.5-1.5 hours (e.g., 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours).

[0044] The graphitization temperature used in this application is a conventional heating procedure. As an example, the first calcination includes: heating to 500°C at 5°C / min, heating to 900°C at 4°C / min, holding at 900°C for 600 min, and then cooling to room temperature for 900 min before discharge. The second calcination includes: heating to 1000°C at 10°C / min, heating to 2500°C at 5°C / min, heating to 2900°C at 2°C / min and holding for 60 min to obtain graphitized coke.

[0045] In step S200, the calcination temperature of the first coating is 800-1500℃ (e.g., 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃).

[0046] In step S200, the rate of heating to the calcination temperature (e.g., 800-1500℃) is 2-8℃ / min (e.g., 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min).

[0047] Step S300 includes: mixing the first coated product with a carbon source at a mass ratio of 100:(0.5-10) (e.g., 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9) to obtain a second mixture; and calcining the second mixture to obtain a second coated product.

[0048] In step S300, the carbon source is selected from one or more of asphalt, starch, glucose, phenolic resin and epoxy resin.

[0049] In step S300, the calcination temperature of the second coating is 900-1400℃ (e.g., 1000℃, 1100℃, 1200℃, 1300℃).

[0050] In step S300, the rate of heating to the calcination temperature (e.g., 900-1400℃) is 2-8℃ / min (e.g., 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min).

[0051] Reagents and materials

[0052] Ethylene glycol, glycerol, DMF, acetic acid, boric acid, urea, and melamine were all analytical grade and sourced from Tianjin Damao Chemical Reagent Factory; dicyandiamide was analytical grade and sourced from Tianjin Guangfu Fine Chemical Research Institute; starch and glucose were analytical grade and sourced from Aladdin.

[0053] the term

[0054] Dv 50 This refers to the particle size at which the cumulative volume distribution percentage reaches 50%, meaning that the volume content of particles smaller than or equal to this size accounts for 50% of the total particle volume.

[0055] The following embodiments are used to further illustrate the advantages and features of this method, and are not intended to limit the invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0056] Unless otherwise specified, the quantitative analysis experiments in the following examples are all repeated three times, and the results are averaged.

[0057] Example 1

[0058] The preparation method of the artificial graphite anode material in this embodiment includes the following steps:

[0059] Pitch coke (Baowu No. 2 negative electrode coke) was crushed to a diameter of less than 1 mm using a roller mill, and then dried in a rotary kiln at 110°C for 4 hours. The dried coke powder was then ground into powder by a mechanical mill to a Dv. 50 =9.5μm, then shaped by a shaping machine to Dv50=11.5μm, and finally calcined at high temperature in a tunnel kiln, with the temperature increased to 500℃ at 5℃ / min, then increased to 900℃ at 4℃ / min, held at 900℃ for 600min, and then cooled to room temperature for 900 minutes to obtain raw material A.

[0060] Raw material A was graphitized in an intermediate frequency furnace at 2900℃. The temperature was increased to 1000℃ at 10℃ / min, to 2500℃ at 5℃ / min, and to 2900℃ at 2℃ / min. The temperature was then held at 2900℃ for 60 min to obtain graphitized product B.

[0061] Boric acid and melamine were added to an ethylene glycol solution at a molar ratio of 2:1, with the molar ratio of boric acid to ethylene glycol being 1:15. After stirring to form a complex, the solution was stirred and evaporated at 130°C until the solution was completely evaporated to obtain the solid-phase precursor C of boron nitride.

[0062] B and C were mixed in a fusion machine at a mass ratio of 100:3 under the conditions of 2000 rpm / min and 15 min to obtain a homogeneous mixture D. The mixture D was then calcined in a tube furnace under an ammonia atmosphere, with the temperature increased to 1300℃ at a rate of 5℃ / min and held at 1300℃ for 4 h to obtain boron nitride-coated graphite E (first coating).

[0063] Boron nitride-coated graphite E was mixed with asphalt (Xinde 250) at a mass ratio of 100:2 in a fusion machine. The mixing conditions were 2000 rpm / min and 15 min. After uniform mixing, the mixture was placed in a roller kiln and calcined at 1150℃ for 600 min under a nitrogen atmosphere (second coating) to obtain artificial graphite anode material F with double coating of boron nitride and carbon layer.

[0064] Example 2

[0065] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that petroleum coke (Daqing coke) is used instead of pitch coke as raw material.

[0066] Example 3

[0067] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that needle coke (Jinzhou needle coke) is used instead of pitch coke as raw material.

[0068] Example 4

[0069] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that petroleum coke calcined coke (Fushun calcined coke) is used instead of pitch coke as raw material.

[0070] Example 5

[0071] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that urea is used instead of melamine as the nitrogen source and glycerol is used instead of ethylene glycol as the solvent to prepare the boron nitride precursor, wherein the molar ratio of boric acid to urea is 1:2.

[0072] Example 6

[0073] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that dicyandiamide is used instead of melamine as the nitrogen source to prepare the boron nitride precursor.

[0074] Example 7

[0075] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that phenolic resin (Yierfu EV-2077D) is used instead of pitch as the carbon source.

[0076] Example 8

[0077] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that the mass ratio of B to C is 100:10 and the mass ratio of E to asphalt is 100:10.

[0078] Example 9

[0079] The preparation method of the artificial graphite anode material in this embodiment is basically the same as that in Example 1, except that the mass ratio of B to C is 100:1 and the mass ratio of E to asphalt is 100:0.5.

[0080] Comparative Example 1

[0081] The preparation method of the artificial graphite anode material in this comparative example differs from that in Example 1 only in that: the preparation and coating steps of the boron nitride precursor are not performed. Instead, graphitized product B and asphalt are directly mixed in a fusion machine at a mass ratio of 100:2. The mixing conditions are 2000 rpm / min and the mixing time is 15 min. After uniform mixing, the mixture is placed in a roller kiln and calcined at 1150°C for 600 min under a nitrogen atmosphere to obtain an artificial graphite anode material with a carbon layer coating.

[0082] Comparative Example 2

[0083] The preparation method of the artificial graphite anode material in this comparative example differs from that in Example 1 only in that the ratio of boric acid to melamine is changed to 1:10, while the other steps remain the same.

[0084] Comparative Example 3

[0085] The preparation method of the artificial graphite anode material in this comparative example differs from that in Example 1 only in that the mass ratio of graphitized product B to the solid precursor C of boron nitride in step D is changed to 100:15.

[0086] Comparative Example 4

[0087] The preparation method of the artificial graphite anode material in this comparative example differs from that in Example 1 only in that the first coating and the second coating are combined into one coating step. Specifically, graphitized product B, boron nitride solid precursor C and pitch are mixed evenly in a mass ratio of 100:3:2.06, and the mixture D is calcined in a tube furnace under an ammonia atmosphere, with the temperature increased to 1300°C at a rate of 5°C / min, and held at 1300°C for 4 hours to obtain an artificial graphite anode material coated with boron nitride precursor and pitch in one step.

[0088] Comparative Example 5

[0089] The preparation method of the artificial graphite anode material in this comparative example differs from that in Example 1 only in that commercially available hexagonal boron nitride (PBN700 from Nitrogen Boron Technology) is used instead of boron nitride solid precursor C.

[0090] Detection Example 1

[0091] The artificial graphite anode materials prepared in the above embodiments and comparative examples were tested according to the following testing methods, and the test results are shown in Table 1 below.

[0092] Volumetric particle size DV of artificial graphite anode materials 50 Detection was performed using a laser method with a Malvern Mastersizer 3000.

[0093] Tap density of artificial graphite anode material: tested using a Dandong Better BT-313 tap density meter;

[0094] Capacity and initial efficiency of artificial graphite anode materials: The Shenzhen Xinwei coin cell battery testing system was used for testing. The testing method was as follows: Artificial graphite anode materials prepared in each example and comparative example were used to prepare electrode sheets. A lithium metal sheet was used as the counter electrode, electrolyte was added, and the materials were assembled into CR2430 coin cells in a vacuum glove box. The charge-discharge steps were as follows: 600 min of rest, 0.1C discharge to 0.005V, 30 min of rest, 0.03C discharge to 0.005V, 30 min of rest, 20 μA to 0.005V, yielding the initial lithium insertion capacity of the artificial graphite anode material. After resting for 120 min, it was charged at 0.1C to 2.0V to complete the first cycle, yielding the initial lithium extraction capacity of the artificial graphite anode material, which is the material capacity. The ratio of the initial lithium extraction capacity to the initial lithium insertion capacity is the initial efficiency.

[0095] Room temperature capacity retention rate: The ratio of the delithiation capacity of a coin cell after 100 cycles at 25℃ to the delithiation capacity of the first cycle is the room temperature capacity retention rate.

[0096] High-temperature capacity retention rate: The ratio of the delithiation capacity of a coin cell after 100 cycles at 55℃ to the delithiation capacity in the first cycle is the high-temperature capacity retention rate.

[0097] Table 1

[0098]

[0099] As can be seen from Table 1, the first efficiency, room temperature capacity retention, and high temperature capacity retention of the carbon coating alone (Comparative Example 1) or the combination of the first coating and the second coating into a single coating step (Comparative Example 4) are significantly lower than those of Example 1. The embodiments of this application improve the first efficiency, room temperature capacity retention, and high temperature capacity retention of the artificial graphite anode material by coating the boron nitride precursor and the carbon source in a two-step coating process.

[0100] As shown in Table 1, changing the parameters for preparing the boron nitride precursor (Comparative Example 2) or using commercially available hexagonal boron nitride (Comparative Example 5) instead of the boron nitride precursor prepared in this application will reduce the first-stage efficiency, room-temperature capacity retention, and high-temperature capacity retention of the prepared artificial graphite anode material to varying degrees. Using the boron nitride precursor prepared in this application for the first coating, the sintered boron nitride coating layer is lamellar, exhibiting a better coating effect compared to commercially available stable boron nitride.

[0101] As shown in Table 1, a higher amount of coating material is not necessarily better; both excessive and insufficient amounts will affect the electrochemical performance of the resulting artificial graphite anode material. In Comparative Example 3, a higher amount of boron nitride reduced the capacity of the resulting artificial graphite anode material.

[0102] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0103] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0104] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing an artificial graphite anode material, characterized in that, include: The preparation of a boron nitride precursor includes: mixing boric acid with a nitrogen source and then adding the mixture to a solvent to form a complex; and heating the complex to evaporate the solvent to obtain the boron nitride precursor, wherein the nitrogen source is selected from one or more of urea, melamine and dicyandiamide. The first coating comprises: mixing graphitized coke with the boron nitride precursor at a mass ratio of 100:(1-10) to obtain a first mixture; and calcining the first mixture to obtain a first coated product; The second coating comprises: mixing the first coating product with a carbon source at a mass ratio of 100:(0.5-10) to obtain a second mixture; and calcining the second mixture to obtain a second coating product.

2. The preparation method according to claim 1, characterized in that, The solvent is selected from one or more of ethylene glycol, glycerol, N,N-dimethylformamide (DMF), and acetic acid; Optionally, the boric acid and the nitrogen source are mixed at a mass ratio of 3:(1-15); Optionally, the boric acid and the nitrogen source are mixed in a mass ratio of 2:(1-4); Optionally, the molar ratio of the boric acid to the solvent is 1:(10-20); Optionally, the preparation of the boron nitride precursor includes: heating the complex at 100-150°C to evaporate the solvent, thereby obtaining the boron nitride precursor; Optionally, the preparation of the boron nitride precursor includes: heating the complex at 120-140°C to evaporate the solvent, thereby obtaining the boron nitride precursor.

3. The preparation method according to claim 1 or 2, characterized in that, The coke is selected from one or more of needle coke, raw petroleum coke, calcined petroleum coke, and pitch coke.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The graphitization includes: a first calcination and a second calcination. The first calcination includes holding the raw material at 800-1000℃ for 8-12 hours. The second calcination includes holding the raw material that has undergone the first calcination at 2800-3000℃ for 0.5-1.5 hours.

5. The preparation method according to claim 4, characterized in that, The graphitization process includes: pretreatment, a first calcination, and a second calcination. The pretreatment includes one or more of crushing, drying, grinding, and shaping to obtain a raw material to be calcined. The particle size Dv of the raw material to be calcined is... 50 It is 6-16μm.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The particle size Dv of the graphitized coke 50 The micrometer diameter is 5-15 μm, and the tap density is 1.0-1.3 g / cm³. 3 .

7. The preparation method according to any one of claims 1 to 6, characterized in that, The carbon source is selected from one or more of asphalt, starch, glucose, phenolic resin and epoxy resin.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The first coating includes: mixing graphitized coke with the boron nitride precursor at a mass ratio of 100:(2-5) to obtain a first mixture; Optionally, the first coating includes: calcining the first mixture at 800-1500°C to obtain the first coated product; Optionally, the first coating includes: calcining the first mixture at 800-1500°C for 2-8 hours to obtain the first coated product; Optionally, the first coating includes: calcining the first mixture at 1000-1400°C to obtain the first coated product; Optionally, the first coating includes calcining the first mixture at 1000-1400°C for 2-8 hours to obtain the first coated product.

9. The preparation method according to claim 8, characterized in that, The heating rate during calcination in the first coating is 2-8℃ / min. Optionally, the heating rate during calcination in the second coating is 2-8 °C / min.

10. The preparation method according to any one of claims 1 to 9, characterized in that, The second coating includes: mixing the first coating product with a carbon source at a mass ratio of 100:(1-5) to obtain a second mixture; Optionally, the second coating includes calcining the second mixture at 900-1400°C to obtain the second coated product.

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