Preparation method of fast-charging graphite negative electrode material based on built-in electric field of heterojunction and negative electrode material

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a preparation method of a fast-charging graphite negative electrode material based on a built-in electric field of a heterojunction and the negative electrode material. The preparation method comprises the following steps: performing activation treatment on graphite to obtain activated graphite; forming a TiO2 sol layer on the surface of the activated graphite through a sol-gel method; filtering, washing and drying the obtained product, and performing heat treatment on the product in an air atmosphere to obtain a graphite intermediate; and performing heat treatment on the graphite intermediate in an ammonia atmosphere, so that the surface layer TiO2 is partially nitrided into TiN, thereby obtaining the graphite negative electrode material. The application can utilize the work function difference between TiO2 and TiN, build a built-in electric field of TiN pointing to TiO2 on the surface of the graphite, provide an ideal driving force, directionally accelerate lithium ion transmission, and improve fast-charging kinetics.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and in particular to a method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field and the anode material itself. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, have become the core choice for modern power battery systems. However, compared to the minute-level charging efficiency of gasoline vehicles, the charging speed of electric vehicles remains one of the key factors restricting their widespread application. The fast-charging capability of power batteries is inherently limited by the internal lithium-ion transport kinetics, exhibiting inherent defects during high-current fast charging: slow interfacial ion transport kinetics and easy lithium deposition, affecting battery reliability and lifespan. Therefore, developing anode materials that combine high energy density, excellent fast-charging performance, and high safety characteristics has become a key research direction for advancing energy storage technology.

[0003] In the structure of lithium-ion batteries, the anode material plays a crucial role. Among them, graphite, with its low operating voltage and excellent layered structure, allows lithium ions to reversibly insert and extract, and its unique physicochemical properties make it the dominant anode material. However, graphite still exhibits some significant problems in practical applications. For example, graphite experiences irreversible capacity loss and SEI film rupture and reformation during charge and discharge, resulting in less than ideal initial charge-discharge efficiency.

[0004] To improve the fast-charging performance of graphite anodes, existing technologies mainly employ surface modification strategies. For example, patent document CN120664539 A discloses a carbon-coated graphite anode material, its preparation method, and its application. This method involves ball milling a nitrogen source, a fluorine source, and graphite, followed by sequential heat treatment and a second heat treatment in the presence of an inert gas to obtain the carbon-coated graphite anode material. While this patent can improve electronic conductivity, it does not effectively regulate Li... + The distribution effect is limited, and the carbon layer may hinder Li + Diffusion. Therefore, how to improve the anode material to directionally accelerate lithium-ion transport and improve fast-charging kinetics remains a key research focus in this field. Summary of the Invention

[0005] In one aspect, this application provides a method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field.

[0006] The technical solution adopted in this application is as follows: A method for preparing a fast-charging graphite anode material based on a heterojunction embedded electric field includes the following steps: Graphite is activated to obtain activated graphite; A TiO2 sol layer is formed on the activated graphite surface using the sol-gel method; The product obtained in step (2) was filtered, washed, dried, and then heat-treated in an air atmosphere to obtain a graphite intermediate. The graphite intermediate is heat-treated in an ammonia atmosphere to partially nitride the surface TiO2 to TiN, thereby obtaining the graphite anode material.

[0007] By employing the above technical solution, the graphite is first activated to remove adsorbed H2O and O2, exposing clean graphite carbon atoms, increasing surface energy, and putting it in an activated state. The sol-gel method is a method that forms a three-dimensional network structure in solution through the hydrolysis and condensation reaction of precursors. This method can form a controllable thickness, continuous, and dense TiO2 amorphous gel layer on graphite particles with complex surfaces. The generated TiO2 gel layer is tightly bonded to the activated graphite surface at the nanoscale. This uniform bonding is crucial for the subsequent formation of uniform heterojunctions. Finally, in an ammonia atmosphere, NH3 decomposes to produce active nitrogen species (such as atomic nitrogen), which undergo a nitriding reaction with TiO2. Since the reaction is a "partial nitriding" starting from the surface, the surface TiO2 gradually transforms into TiN, while the inner layer remains TiO2, thus forming a tightly contacted TiN / TiO2 heterojunction in situ within the coating layer of a single particle.

[0008] Due to the Fermi level difference, charge transfer occurs between the formed TiN (conductive phase) and the unreacted TiO2 (semiconductor phase) at the interface, creating a built-in electric field pointing from TiO2 to TiN. During discharge (lithium-ion insertion into graphite), the negative electrode surface is negatively charged, and the direction of the electric field favors the rapid migration of positively charged Li⁺ to the graphite surface. During charging (lithium removal), it similarly promotes the rapid extraction of Li⁺ from graphite, thus accelerating the lithium-ion interface kinetics in both directions. Furthermore, TiN is an excellent electronic conductor, and its surface coating significantly improves the electronic conductivity of the entire particle surface; the internal TiO2 provides a stable structural framework and ion transport channels. The combination of these two elements optimizes both electron and ion transport.

[0009] In some embodiments of this application, in step (2), the sol-gel method includes the following preparation steps: dissolving tetrabutyl titanate in anhydrous ethanol, stirring evenly, then slowly adding dilute acetic acid solution and stirring to form a transparent TiO2 sol, then adding activated graphite to the obtained TiO2 sol solution, and ultrasonically dispersing evenly, and continuously stirring in a water bath at 50-60°C so that the TiO2 sol coats the graphite surface.

[0010] By employing the above technical solution, tetrabutyl titanate is used as a hydrolyzable Ti source, anhydrous ethanol is used as a solvent to ensure controllable hydrolysis, dilute acetic acid is used as a catalyst to obtain a stable transparent sol, ultrasonic dispersion ensures that graphite is fully deagglomerated in the sol, and a 50-60℃ water bath promotes sol-gel conversion and improves coating efficiency. Overall, this method ensures that the TiO2 precursor can be uniformly and continuously coated on the graphite surface, laying the foundation for the formation of homogeneous heterojunctions.

[0011] In some embodiments of this application, in step (1), the graphite is activated by the following method: the graphite is placed in an inert gas atmosphere, heated to 500-550°C, kept at that temperature for 1-3 hours, and then naturally cooled to room temperature to obtain the activated graphite.

[0012] By adopting the above technical solution, heat treatment at 500-550℃ in an inert atmosphere can effectively remove impurities, water vapor and some oxygen-containing functional groups physically adsorbed on the graphite surface, exposing a cleaner and more active carbon surface, while avoiding high-temperature oxidation of graphite in air. The above "activation" treatment mainly enhances the physical adsorption and interfacial compatibility between graphite and the subsequent TiO2 layer.

[0013] In some embodiments of this application, in step (3), the obtained product is first dried at 80-100°C, and then heated to 400-450°C in an air atmosphere, kept at that temperature for 2-3 hours, and then cooled naturally to obtain the graphite intermediate.

[0014] By adopting the above technical solution, drying at 80-100℃ gently removes the solvent and prevents the gel layer from cracking due to rapid water loss; heat treatment in air at 400-450℃ causes amorphous TiO2 to crystallize into anatase phase, which has the advantage of high activity and is beneficial for subsequent nitriding. At the same time, this temperature also promotes possible CO-Ti chemical bonding between the graphite surface and TiO2, significantly strengthening the interfacial bonding force.

[0015] In some embodiments of this application, the concentration of tetrabutyl titanate is 0.07-0.22 M, and the concentration of the dilute acetic acid aqueous solution is 0.5 M-1 M.

[0016] By employing the above technical solution, the concentration of tetrabutyl titanate directly determines the final thickness of the TiO2 coating layer. If the concentration is too low, the coating layer will be too thin or discontinuous, resulting in a weak heterojunction effect; if the concentration is too high, the coating layer will be too thick, increasing the lithium-ion diffusion distance and making it prone to stress cracking. A dilute acetic acid aqueous solution controls the pH value and gelation rate of the sol, affecting the stability of the sol and the uniformity of the coating. This concentration range can effectively catalyze the reaction, obtaining a stable sol suitable for coating.

[0017] In some embodiments of this application, in step (4), the flow rate of ammonia is 150-300 sccm, the nitriding temperature is 500-600 ℃, and the nitriding time is 1-2 h.

[0018] By adopting the above technical solution, the ammonia gas flow rate ensures that the reaction atmosphere is sufficient and updated in a timely manner, so that the nitriding reaction proceeds uniformly. By controlling the temperature and time, NH3 can partially nitrid the surface TiO2 to form a gradient structure in which the TiN content decreases from the surface to the inside, rather than completely converting it into TiN, thus successfully constructing a heterojunction with a strong built-in electric field.

[0019] In some embodiments of this application, the heating rate during the heat treatment process is 2-5°C / min.

[0020] By adopting the above technical solution and controlling the heating rate, it can reduce the thermal stress between the graphite substrate, TiO2 coating and reaction vessel, prevent coating cracking and peeling caused by mismatch in thermal expansion coefficients, and thus ensure the integrity of the heterojunction structure.

[0021] In some embodiments of this application, the conditions for ultrasonic dispersion are: ultrasonic dispersion for 30-40 minutes, power 300-350W, and frequency 10-40kHz.

[0022] By adopting the above technical solution, the graphite aggregates can be better dispersed, allowing them to exist in the sol as single particles or micro-agglomerates.

[0023] In some embodiments of this application, the graphite D50 is 13-16 μm and the specific surface area is 1-2 m2 / g.

[0024] By adopting the above technical solution and selecting graphite, the high tap density and energy density of the material are ensured.

[0025] In summary, this application includes at least one of the following beneficial effects: 1. This method introduces a key built-in electric field by constructing a TiN / TiO2 heterojunction coating layer on the graphite surface. This electric field originates from the work function difference and charge rearrangement between TiN (metallic conductivity) and TiO2 (n-type semiconductor). During lithiation / delithiation, this built-in electric field can: directionally attract lithium ions, reducing the energy barrier for them to cross the interface; promote interface charge separation and transport, reducing charge transfer impedance; and improve surface reaction kinetics, achieving more uniform and faster lithium ion insertion / extraction. Attached Figure Description

[0026] Figure 1 This is a charge diagram of the TiN / TiO2 heterojunction in this application. Detailed Implementation

[0027] The present application will be further described in detail below with reference to the embodiments. Example 1

[0028] This embodiment discloses a method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field, which specifically includes the following steps: (1) Take 20g of artificial graphite (graphite D50 is 13-16μm and specific surface area is 1-2m²) 2 / g) was placed in an inert atmosphere (Ar), heated to 500°C at 5°C / min, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain an activated graphite surface; (2) Dissolve 2.0 mL of tetrabutyl titanate (TBOT) in 40 mL of anhydrous ethanol and stir magnetically until homogeneous. Then slowly add 1 mL of dilute acetic acid aqueous solution and stir vigorously to form a stable transparent TiO2 sol. Disperse the obtained activated graphite in the TiO2 sol and perform ultrasonic dispersion at a power of 300 W and a frequency of 20 kHz to make the graphite uniformly dispersed. Stir continuously in a 60°C water bath for 6 h to allow the sol to slowly gel and coat the graphite surface. (3) The obtained sample was vacuum filtered, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. After that, the dried sample was placed in a muffle furnace and heated to 450°C at 2°C / min in air atmosphere, held for 2 hours, and then cooled naturally to obtain TiO2-coated graphite intermediate; (4) Take 20g of TiO2-coated graphite intermediate and place it in a tube furnace. Under an ammonia (NH3) atmosphere (flow rate 200sccm), heat it to 500℃ at 5℃ / min and hold it for 1 hour, then let it cool naturally. Under these conditions, the surface TiO2 is partially nitrided to TiN, while the inner TiO2 bonded to graphite is retained, thus forming a TiN / TiO2 heterojunction at the interface to obtain a fast-charging graphite anode material. Example 2

[0029] This embodiment discloses a method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field, which specifically includes the following steps: (1) Take 20g of artificial graphite (graphite D50 is 13-16μm and specific surface area is 1-2m²) 2 / g) was placed in an inert atmosphere (Ar), heated to 500°C at 5°C / min, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain an activated graphite surface; (2) Dissolve 1.0 mL of tetrabutyl titanate (TBOT) in 40 mL of anhydrous ethanol and stir magnetically until homogeneous. Then slowly add 1 mL of dilute acetic acid aqueous solution and stir vigorously to form a stable transparent TiO2 sol. Disperse the obtained activated graphite in the TiO2 sol and perform ultrasonic dispersion at a power of 300 W and a frequency of 20 kHz to make the graphite uniformly dispersed. Stir continuously in a 60°C water bath for 6 h to allow the sol to slowly gel and coat the graphite surface. (3) The obtained sample was vacuum filtered, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. After that, the dried sample was placed in a muffle furnace and heated to 450°C at 2°C / min in air atmosphere, held for 2 hours, and then cooled naturally to obtain TiO2-coated graphite intermediate; (4) Take 20g of TiO2-coated graphite intermediate and place it in a tube furnace. Under an ammonia (NH3) atmosphere (flow rate 200sccm), heat it to 500℃ at 5℃ / min and hold it for 1 hour, then let it cool naturally. Under these conditions, the surface TiO2 is partially nitrided to TiN, while the inner TiO2 bonded to graphite is retained, thus forming a TiN / TiO2 heterojunction at the interface to obtain a fast-charging graphite anode material. Example 3

[0030] This embodiment discloses a method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field, which specifically includes the following steps: (1) Take 20g of artificial graphite (graphite D50 is 13-16μm and specific surface area is 1-2m²) 2 / g) was placed in an inert atmosphere (Ar), heated to 500°C at 5°C / min, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain an activated graphite surface; (2) Dissolve 3.0 mL of tetrabutyl titanate (TBOT) in 40 mL of anhydrous ethanol and stir magnetically until homogeneous. Then slowly add 1 mL of dilute acetic acid aqueous solution and stir vigorously to form a stable transparent TiO2 sol. Disperse the obtained activated graphite in the TiO2 sol and perform ultrasonic dispersion at a power of 300 W and a frequency of 20 kHz to make the graphite uniformly dispersed. Stir continuously in a 60°C water bath for 6 h to allow the sol to slowly gel and coat the graphite surface. (3) The obtained sample was vacuum filtered, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. After that, the dried sample was placed in a muffle furnace and heated to 450°C at 2°C / min in air atmosphere, held for 2 hours, and then cooled naturally to obtain TiO2-coated graphite intermediate; (4) Take 20g of TiO2-coated graphite intermediate and place it in a tube furnace. Under an ammonia (NH3) atmosphere (flow rate 200sccm), heat it to 500℃ at 5℃ / min and hold it for 1 hour, then let it cool naturally. Under these conditions, the surface TiO2 is partially nitrided to TiN, while the inner TiO2 bonded to graphite is retained, thus forming a TiN / TiO2 heterojunction at the interface to obtain a fast-charging graphite anode material.

[0031] Comparative Example 1 This comparative example discloses a method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field, which specifically includes the following steps: (1) Take 20g of artificial graphite (graphite D50 is 13-16μm and specific surface area is 1-2m²) 2 / g) was placed in an inert atmosphere (Ar), heated to 500°C at 5°C / min, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain an activated graphite surface; (2) Dissolve 2.0 mL of tetrabutyl titanate (TBOT) in 40 mL of anhydrous ethanol and stir magnetically until homogeneous. Then slowly add 1 mL of dilute acetic acid aqueous solution and stir vigorously to form a stable transparent TiO2 sol. Disperse the obtained activated graphite in the TiO2 sol and perform ultrasonic dispersion at a power of 300 W and a frequency of 20 kHz to make the graphite uniformly dispersed. Stir continuously in a 60°C water bath for 6 h to allow the sol to slowly gel and coat the graphite surface. (3) The obtained sample was vacuum filtered, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. After that, the dried sample was placed in a muffle furnace and heated to 450°C at 2°C / min in an air atmosphere, held for 2 hours, and then cooled naturally to obtain TiO2-coated graphite intermediate.

[0032] Comparative Example 2 This comparative example discloses a method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field, which specifically includes the following steps: (1) Take 20g of artificial graphite (graphite D50 is 13-16μm and specific surface area is 1-2m²) 2 / g) was placed in an inert atmosphere (Ar), heated to 500°C at 5°C / min, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain an activated graphite surface; (2) Dissolve 2.0 mL of tetrabutyl titanate (TBOT) in 40 mL of anhydrous ethanol and stir magnetically until homogeneous. Then slowly add 1 mL of dilute acetic acid aqueous solution and stir vigorously to form a stable transparent TiO2 sol. Disperse the obtained activated graphite in the TiO2 sol and perform ultrasonic dispersion at a power of 300 W and a frequency of 20 kHz to make the graphite uniformly dispersed. Stir continuously in a 60°C water bath for 6 h to allow the sol to slowly gel and coat the graphite surface. (3) The obtained sample was vacuum filtered, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. After that, the dried sample was placed in a muffle furnace and heated to 450°C at 2°C / min in air atmosphere, held for 2 hours, and then cooled naturally to obtain TiO2-coated graphite intermediate; (4) Take 20g of TiO2-coated graphite intermediate and put it into a tube furnace. Under an ammonia (NH3) atmosphere (flow rate 200sccm), heat it to 600℃ at 5℃ / min, keep it at that temperature for 2 hours, and then cool it naturally to obtain the graphite anode material.

[0033] Performance testing The electrode was prepared using a wet coating process. 85% of the graphite anode material obtained above, 5% Super P, and 10% binder (carboxymethyl cellulose CMC and aqueous binder LA136D) were mixed into a uniform slurry. This slurry was coated onto copper foil and dried at 80°C for 12 hours. Subsequently, it was transferred to a vacuum drying oven and vacuum dried at 60°C for 12 hours to remove residual oxygen and moisture, yielding a dry electrode film. The average areal density of the electrode active material was approximately 1.7 mg / cm².

[0034] Electrochemical performance tests were conducted using CR2032 coin cells. The cells were assembled in an argon-atmospheric glove box (oxygen and water content were both below 0.1 ppm). During half-cell assembly, the parameters for each component were as follows: a Celgard 2500 membrane was used as the separator, lithium metal foil as the counter electrode, and the electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) solution. This electrolyte used a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) as a co-solvent (volume ratio = 2:1:2), with 10 wt.% of fluoroethylene carbonate (FEC) added as a functional additive.

[0035] The batteries prepared with the negative electrode materials of Examples 1-3 and Comparative Examples 1-2 were tested for their first charge-discharge efficiency, 5C capacity retention, 3C cycle stability (1200 cycles), and charge transfer impedance Rct (Ω). The test results are shown in the table below.

[0036] Example 1 94% 86% 87% 7 Example 2 91% 81% 83% 10 Example 3 90% 83% 80% 21 Comparative Example 1 93% 67% 74% 72 Comparative Example 2 89% 76% 72% 37 Comparing Example 1 (TBOT 2.0 mL + nitriding at 500℃ for 1 h) with Comparative Example 1, Example 1 exhibited better performance across all aspects, with a charge transfer impedance (Rct) of 7 Ω, a significant reduction compared to Comparative Example 1 (pure TiO2 coating, 72 Ω). This significant improvement is primarily attributed to the directional built-in electric field formed at the heterojunction interface, which provides additional driving force for lithium-ion migration.

[0037] Specifically, the difference in work function between TiO2 (work function approximately 5.21 eV) and TiN (work function approximately 4.74 eV) induces a space charge region at the interface pointing from TiN to TiO2, effectively reducing the interfacial energy barrier for lithium-ion intercalation into graphite. Simultaneously, the high electronic conductivity of TiN and the good ionic conductivity of TiO2 complement each other, achieving synergistic optimization of "electronic conduction-ion transport-interface stability." In terms of rate performance, this synergistic effect is reflected in Example 1 achieving a capacity retention of 86% at 5C, significantly higher than the 67% of Comparative Example 1, demonstrating a marked improvement in fast-charging capability.

[0038] Precise control of the coating thickness and nitriding conditions is key to achieving the aforementioned superior performance. The amount of TBOT directly determines the thickness of the TiO2 layer: when the amount is 1.0 mL (Example 2), the TiO2 coating layer is thinner than in Example 1, the heterojunction interface is limited, the built-in electric field effect is weak, and Rct increases to 10 Ω; while when the amount is 3.0 mL (Example 3), the coating layer is thicker, although the heterojunction interface is sufficient, the excessively long ion transport path causes Rct to increase to 21 Ω, and the cycling stability decreases to 80% (1200 cycles).

[0039] The nitriding conditions affect the ratio of TiN to TiO2: In Comparative Example 2, after nitriding at 600℃ for 2 hours, the material was completely converted to TiN. Although the increased electronic conductivity reduced Rct to 37 Ω, its initial efficiency dropped to 89% and cycle retention was only 72%, indicating that while complete nitriding is beneficial for electron transport, it sacrifices interfacial stability and lithium-ion affinity. In contrast, Example 1, using a nitriding process at 500℃ for 1 hour, achieved a gradient heterojunction structure with partial nitriding of the surface layer and retention of TiO2 in the inner layer. This ensured high electronic conductivity through the surface TiN layer and maintained good ion transport and interfacial stability through the inner TiO2 layer. Ultimately, the material maintained a capacity retention of 87% and an initial efficiency of 94% after 1200 cycles, demonstrating the best overall performance. This indicates that by precisely coordinating the coating thickness and nitriding degree, synergistic optimization of electron-ion transport can be achieved, providing an effective material solution for developing high-performance fast-charging lithium-ion battery anodes.

[0040] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing a fast-charging graphite anode material based on a heterojunction embedded electric field, characterized in that: Includes the following steps: Graphite is activated to obtain activated graphite; A TiO2 sol layer is formed on the activated graphite surface using the sol-gel method; The product obtained in step (2) was filtered, washed, dried, and then heat-treated in an air atmosphere to obtain a graphite intermediate. The graphite intermediate is heat-treated in an ammonia atmosphere to partially nitride the surface TiO2 to TiN, thereby obtaining the graphite anode material.

2. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 1, characterized in that: In step (2), the sol-gel method includes the following preparation steps: dissolve tetrabutyl titanate in anhydrous ethanol, stir evenly, then slowly add dilute acetic acid solution and stir to form transparent TiO2 sol, then add activated graphite to the obtained TiO2 sol solution, and ultrasonically disperse evenly, and continuously stir in a water bath at 50-60℃ so that TiO2 sol coats the graphite surface.

3. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 2, characterized in that: In step (1), the graphite is activated by the following method: the graphite is placed in an inert gas atmosphere, heated to 500-550°C, kept at that temperature for 1-3 hours, and then naturally cooled to room temperature to obtain the activated graphite.

4. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 2, characterized in that: In step (3), the obtained product is first dried at 80-100℃, and then heated to 400-450℃ in an air atmosphere, kept at that temperature for 2-3 hours, and then cooled naturally to obtain the graphite intermediate.

5. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 2, characterized in that: The concentration of the tetrabutyl titanate is 0.07-0.22 M, and the concentration of the dilute acetic acid aqueous solution is 0.5 M-1 M.

6. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 1, characterized in that: In step (4), the flow rate of ammonia is 150-300 sccm, the nitriding temperature is 500-600 ℃, and the nitriding time is 1-2 h.

7. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 6, characterized in that: During the heat treatment process, the heating rate is 2-5 °C / min.

8. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 2, characterized in that: The conditions for ultrasonic dispersion are: ultrasonic dispersion for 30-40 minutes, power 300-350W, and frequency 10-40kHz.

9. The method for preparing a fast-charging graphite anode material based on a heterojunction built-in electric field according to claim 3, characterized in that: The graphite has a D50 of 13-16 μm and a specific surface area of ​​1-2 m². 2 / g.

10. A negative electrode material, characterized in that: It is prepared using the preparation method of any one of claims 1-9.

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