Nitrogen-doped artificial graphite negative electrode material, and preparation method and application thereof

Abstract

The application discloses a kind of nitrogen-doped artificial graphite negative electrode materials and preparation method and application thereof, steps include: the raw material coke is pretreated, and artificial graphite is obtained by graphitization;Artificial graphite is compounded with nitrogen source under alkaline conditions, and calcination, and the negative electrode material is obtained.This unique preparation method can introduce nitrogen element into artificial graphite, and this introduction makes the molecular structure of the ink sheet change, and enhances the contact between layers.Compared with the lithium ion battery in the past, the lithium ion battery containing this nitrogen-doped artificial graphite negative electrode material improves the discharge specific capacity while significantly prolonging the cycle life.

Description

A nitrogen-doped artificial graphite anode material, its preparation method and application Technical Field

[0001] This invention belongs to the field of graphite anode materials, and particularly relates to a nitrogen-doped graphite anode material, its preparation method, and its application. Background Technology

[0002] Due to the dwindling resources of fossil fuels and the severe environmental pollution caused by their use, the government is vigorously supporting and developing the new energy industry to conserve resources and protect the environment. Among these industries, lithium-ion battery storage is one of the fastest-growing sectors, and graphite anodes, as key materials determining the rate performance and cycle life of lithium-ion batteries, have naturally attracted widespread attention.

[0003] Among these, artificial graphite, as a negative electrode material for lithium-ion batteries, exhibits excellent cycle performance and safety, resulting in its production share exceeding 60%. Furthermore, artificial graphite boasts mature manufacturing processes and a significant price advantage, making it the mainstream negative electrode material. However, in practical applications, the cycle performance of lithium-ion batteries made from artificial graphite materials used in energy storage has not met expectations, and the battery capacity requires further improvement. In lithium-ion energy storage battery systems, the negative electrode is crucial in determining the battery's cycle life; therefore, when artificial graphite is used to construct the negative electrode, its electrochemical performance becomes particularly important. However, considering the interdependent relationships among various technical indicators of artificial graphite negative electrode materials, developing a high-performance artificial graphite negative electrode material has become a pressing issue for the development of lithium-ion batteries. Summary of the Invention

[0004] To address the technical problems existing in the background art, this application discloses a nitrogen-doped graphite anode material, its preparation method, and its application. By combining artificial graphite with a nitrogen source under alkaline conditions and calcining it, nitrogen element is introduced, thereby changing the molecular structure of the graphite flakes in the obtained anode material and enhancing the connection between layers, ultimately improving the capacity and cycle life of the obtained lithium-ion battery.

[0005] This invention proposes a nitrogen-doped artificial graphite anode material, comprising the following steps:

[0006] S1. After graphitizing the raw material coke, artificial graphite is obtained;

[0007] S2. The artificial graphite is compounded with a nitrogen source under alkaline conditions and then calcined to obtain the negative electrode material.

[0008] In this invention, raw coke is graphitized to obtain artificial graphite with a regular structure. After the artificial graphite is compounded with a nitrogen source under alkaline conditions and calcined, nitrogen can be introduced into the interior of the graphite, changing the molecular structure of the graphite flakes and enhancing the connection between the layers. Since the graphitization temperature is high, the nitrogen can be incorporated after the raw coke is graphitized to prepare artificial graphite, which can avoid the loss of nitrogen caused by the high temperature of graphitization.

[0009] Preferably, in step S1, the raw material coke is at least one of needle coke, sponge coke, or petroleum coke.

[0010] In this invention, when using raw coke as the main carbon source, needle coke, sponge coke, or petroleum coke have high coke content and few impurities, making them very suitable for preparing artificial graphite.

[0011] Preferably, in step S1, before the graphitization of the raw material coke, the method further includes granulating the raw material coke with a binder;

[0012] Preferably, the binder is at least one of petroleum asphalt, natural asphalt, or coal tar pitch;

[0013] Preferably, the amount of binder is 8-12% of the mass of the raw coke.

[0014] In this invention, asphalt is both a carbon source and a binder. When exposed to high temperatures, the asphalt softens and begins to flow, allowing it to better encapsulate the raw coke particles.

[0015] In this invention, when the amount of binder accounts for 8-12% of the mass of the raw coke, the binder can effectively bind the raw coke together.

[0016] Preferably, in step S1, the graphitization temperature is 2800-3200℃;

[0017] Preferably, the D50 particle size of the artificial graphite is 15-17 μm.

[0018] In this invention, graphitization is used to rearrange the carbon atoms in the mixture of raw material coke and pitch at high temperature to form a regular graphite crystal structure. Among them, the artificial graphite structure with a particle size of 15-17μm is relatively stable and can better withstand the volume changes caused by lithium ion insertion and extraction, which is beneficial to extending the cycle life of the battery.

[0019] Preferably, in step S2, the nitrogen source is at least one of polyvinylpyrrolidone or 2-methylimidazole.

[0020] Preferably, in step S2, the composite process specifically includes: mixing artificial graphite, a nitrogen source, and an alkaline solution to form a paste;

[0021] Preferably, the pH of the alkaline solution is 9-10, and it is preferably a KOH or NaOH solution.

[0022] In this invention, compared to previous nitrogen doping methods that simply involved directly combining artificial graphite with a nitrogen source and then calcining it, this invention combines artificial graphite with a nitrogen source under alkaline conditions and then calcines it. The latter method can more effectively alter the molecular structure of the graphite flakes and enhance the bonding between layers.

[0023] This is because inorganic alkalis induce voids in artificial graphite at high temperatures. These voids make it easier for nitrogen sources to enter the graphite interior for doping, thereby altering the structure of the graphite flake molecules. Therefore, the nitrogen doping described in this invention not only occurs on the surface of graphite but also penetrates deep into the graphite flake molecules. The nitrogen atoms doped inside and outside the graphite form a conductive network with the graphite itself. The presence of this conductive network enhances the connection between layers, thereby effectively reducing the damage to the graphite structure caused by lithium ions during insertion and extraction.

[0024] Preferably, in step S2, before the composite process, the method further includes: subjecting artificial graphite to a substitution condensation reaction with chloroacetic acid to obtain carboxylated artificial graphite.

[0025] In this invention, the artificial graphite is substituted with chloroacetic acid to form artificial graphite with carboxyl groups on its surface, thereby increasing the surface polarity of the artificial graphite. When it is subsequently combined with a nitrogen source such as polyvinylpyrrolidone or 2-methylimidazole, it can form an effective hydrogen bond adsorption effect on both, which promotes the effective coating of polyvinylpyrrolidone or 2-methylimidazole on the surface of the artificial graphite. This facilitates the calcination of the latter to form a tightly bonded nitrogen-doped carbon shell, further improving the electrochemical performance of the resulting negative electrode material.

[0026] Preferably, in step S2, the calcination temperature is 700-900℃;

[0027] Preferably, the calcination is carried out under inert gas conditions.

[0028] In this invention, the calcination temperature of 700-900℃ simultaneously satisfies the requirements of nitrogen doping and carbonization of the nitrogen source, while the inert atmosphere is used to avoid oxidation.

[0029] The present invention also proposes a nitrogen-doped artificial graphite anode material, which is obtained by the above preparation method.

[0030] The present invention also proposes a lithium-ion battery comprising the above-mentioned nitrogen-doped artificial graphite anode material.

[0031] The beneficial effects of this invention are:

[0032] (1) By doping artificial graphite with nitrogen, the discharge specific capacity of lithium-ion batteries containing such artificial graphite anode material is improved.

[0033] (2) By introducing nitrogen through a unique doping method, the structure of artificial graphite sheet molecules is changed, the connection between layers is enhanced, and the capacity and cycle life of lithium-ion batteries are ultimately improved. Attached Figure Description

[0034] Figure 1 is a 500x scanning electron microscope image of the nitrogen-doped artificial graphite anode material prepared in Example 1;

[0035] Figure 2 is a 3000x scanning electron microscope image of the nitrogen-doped artificial graphite anode material prepared in Example 1. Detailed Implementation

[0036] Example 1

[0037] This embodiment proposes a nitrogen-doped artificial graphite anode material, and the specific method includes the following steps:

[0038] (1) Petroleum coke (volatile matter ≤15%) was crushed and ground to obtain sample A, with a D50 of 10.21 μm; coal tar pitch (softening point 150℃) was added to sample A at a ratio of 10 wt% of sample A, and granulated at 550℃ to obtain sample B, with a D50 of 19.60 μm; sample B was graphitized at 2950℃ to obtain sample C, with a D50 of 16.47 μm;

[0039] (2) After mixing sample C and PVP powder at a mass ratio of 5:1, add 3 times the mass of PVP powder in pH=10 KOH solution, stir and mix to form a paste, and then calcine at 800℃ in a nitrogen atmosphere to obtain sample D.

[0040] (3) After washing sample D with deionized water, it was dried in an oven at 80°C for 12 hours. After grinding the dried sample, sample E was obtained, which is the nitrogen-doped artificial graphite anode material.

[0041] The artificial graphite anode material obtained in the above embodiments was tested by scanning electron microscopy, and the results are shown in Figures 1 and 2. Referring to Figures 1 and 2, it can be seen that the nitrogen-doped artificial graphite anode material in the embodiments has a multi-folded sheet structure.

[0042] Example 2

[0043] This embodiment proposes a nitrogen-doped artificial graphite anode material, and the specific method includes the following steps:

[0044] (1) Petroleum coke (volatile matter ≤15%) was crushed and ground to obtain sample A, with a D50 of 10.21 μm; coal tar pitch (softening point 150℃) was added to sample A at a ratio of 10 wt% of sample A, and granulated at 550℃ to obtain sample B, with a D50 of 19.60 μm; sample B was graphitized at 2950℃ to obtain sample C, with a D50 of 16.47 μm;

[0045] (2) After mixing sample C and 2-methylimidazole at a mass ratio of 5:1, add 3 times the mass of 2-methylimidazole in pH=10 KOH solution, stir and mix to form a paste, and then calcine at 800℃ in a nitrogen atmosphere to obtain sample D;

[0046] (3) After washing sample D with deionized water, it was dried in an oven at 80°C for 12 hours. After grinding the dried sample, sample E was obtained, which is the nitrogen-doped artificial graphite anode material.

[0047] Example 3

[0048] This embodiment proposes a nitrogen-doped artificial graphite anode material, and the specific method includes the following steps:

[0049] (1) Petroleum coke (volatile matter ≤15%) was crushed and ground to obtain sample A, with a D50 of 10.21 μm; coal tar pitch (softening point 150℃) was added to sample A at a ratio of 8 wt% of sample A, and granulation was carried out at 650℃ to obtain sample B, with a D50 of 18.79 μm; sample B was graphitized at 3200℃ to obtain sample C, with a D50 of 15.84 μm;

[0050] (2) After mixing sample C and PVP powder at a mass ratio of 10:1, add 3 times the mass of PVP powder in pH=10 KOH solution, stir and mix to form a paste, and then calcine at 900℃ in a nitrogen atmosphere to obtain sample D.

[0051] (3) After washing sample D with deionized water, it was dried in an oven at 80°C for 12 hours. After grinding the dried sample, sample E was obtained, which is the nitrogen-doped artificial graphite anode material.

[0052] Example 4

[0053] This embodiment proposes a nitrogen-doped artificial graphite anode material, and the specific method includes the following steps:

[0054] (1) Petroleum coke (volatile matter ≤15%) was crushed and ground to obtain sample A, with a D50 of 10.21 μm; coal tar pitch (softening point 150℃) was added to sample A at a ratio of 12 wt% of sample A, and granulated at 500℃ to obtain sample B, with a D50 of 20.32 μm; sample B was graphitized at 2800℃ to obtain sample C, with a D50 of 17.51 ​​μm;

[0055] (2) After mixing sample C and PVP powder at a mass ratio of 10:3, add 3 times the mass of PVP powder in pH=10 KOH solution, stir and mix to form a paste, and calcine at 700℃ in a nitrogen atmosphere to obtain sample D.

[0056] (3) After washing sample D with deionized water, it was dried in an oven at 80°C for 12 hours. Then, the dried sample was ground into powder to obtain sample E, which is the nitrogen-doped artificial graphite anode material.

[0057] Example 5

[0058] This embodiment proposes a nitrogen-doped artificial graphite anode material, and the specific method includes the following steps:

[0059] (1) Petroleum coke (volatile matter ≤15%) was crushed and ground to obtain sample A, with a D50 of 10.21 μm; coal tar pitch (softening point 150℃) was added to sample A at a ratio of 10 wt% of sample A, and granulated at 550℃ to obtain sample B, with a D50 of 19.60 μm; sample B was graphitized at 2950℃ to obtain sample C, with a D50 of 16.47 μm;

[0060] (2) After adding sample C to water and dispersing it evenly by ultrasonication, add 10 wt% KOH and 5 wt% chloroacetic acid of sample C. After ultrasonic reaction at 60℃ for 6 hours, filter and dry to obtain sample D. Mix sample D and 2-methylimidazole at a mass ratio of 5:1, add 3 times the mass of 2-methylimidazole in pH=10 KOH solution, stir and mix to form a paste, and calcine at 800℃ in a nitrogen atmosphere to obtain sample E.

[0061] (3) After washing sample E with deionized water, it is dried in an oven at 80°C for 12 hours. After grinding the dried sample, sample F is obtained, which is the nitrogen-doped artificial graphite anode material.

[0062] Comparative Example 1

[0063] This comparative example proposes an artificial graphite anode material. The specific method is as described in step (1) of Example 1. After obtaining sample C, it is the artificial graphite anode material.

[0064] Comparative Example 2

[0065] This comparative example proposes an artificial graphite anode material, the specific method of which includes the following steps:

[0066] (1) Petroleum coke (volatile matter ≤15%) was crushed and ground to obtain sample A, with a D50 of 10.21 μm; coal tar pitch (softening point 150℃) and PVP powder were added to sample A and mixed evenly, with the coal tar pitch added at a ratio of 10 wt% and the PVP powder added at a ratio of 20 wt%; after granulation at 550℃, sample B was obtained, with a D50 of 22.25 μm; sample B was graphitized at 2950℃ to obtain sample C, with a D50 of 18.24 μm;

[0067] (2) After washing sample C with deionized water, it was dried in an oven at 80°C for 12 hours. Then, the dried sample was ground into powder to obtain sample D, which is the artificial graphite anode material.

[0068] Comparative Example 3

[0069] This comparative example proposes an artificial graphite anode material. The specific method is the same as in Example 1, except that in step (2), sample C and PVP powder are mixed at a mass ratio of 5:1, and then water with a mass of 3 times that of PVP powder is added. After stirring and mixing to form a paste, the paste is calcined at 800°C in a nitrogen atmosphere to obtain sample D.

[0070] The particle size, tap density, specific surface area, and degree of graphitization of the artificial graphite materials obtained in the above embodiments and comparative examples were tested:

[0071] During particle size testing, artificial graphite material is dispersed in ethanol using ultrasonic vibration, and then the dispersed sample is placed in the sample cell of the Malvern 3000 laser particle size analyzer, and the instrument is started for measurement.

[0072] During the tap density test, the artificial graphite negative electrode material is poured into the sample tube of the tap density meter. After tapping at a vibration frequency of 200 times / minute, a vibration amplitude of 8mm, and a tapping time of 20min, the height h of the sample inside the sample tube is measured using calipers, and the inner diameter r of the sample tube is recorded. The tap density is calculated using the density formula: ρ = m / πr. 2 h;

[0073] The specific surface area was measured using the gas adsorption BET method, and the Micromeritics ASAP3020 specific surface area and pore size analyzer was used for the test.

[0074] The degree of graphitization was tested using an X-ray powder diffractometer (model: Shimadzu XRD-7000). The target material was a Cu (copper) target, the X-ray tube voltage was 35kV, the current was 35mA, the scanning angle range (2θ) was 5°-90°, the scanning step size was 0.01°, and the duration of each step was 2s. At the same time, silicon powder accounting for 15% of the mass of the artificial graphite material was added. Based on the principle of the internal standard method, the peak position of the silicon standard was used to calibrate the instrument and test error, thereby accurately calculating the characteristic peak position of the negative electrode material and obtaining the degree of graphitization.

[0075] Table 1. Physical performance test results of the artificial graphite anode materials described in the embodiments and comparative examples.

[0076]

[0077] The electrochemical properties of the artificial graphite materials obtained in the above embodiments and comparative examples were tested:

[0078] The artificial graphite anode material, conductive agent (acetylene black), binder (polyvinylidene fluoride, PVDF), and solvent (N-methylpyrrolidone, NMP) described in the above embodiments or comparative examples are stirred evenly to form a slurry, wherein the mass ratio of artificial graphite anode material, acetylene black, and polyvinylidene fluoride is 8:1:1; the slurry is coated on a copper foil current collector, then dried to remove the solvent, and then rolled to obtain the anode sheet;

[0079] Using the aforementioned negative electrode as the working electrode and a lithium metal sheet as the counter electrode, the assembly operation was carried out in a glove box using a separator (polypropylene separator) and electrolyte. The electrolyte was a 1 mol / L LiPF6 solution with a solvent ratio of DMC + EMC + EC = 1:1:1, and the mass ratio of electrolyte to negative electrode was 4:1. The assembly environment was kept dry and oxygen-free to obtain a lithium-ion battery. A battery testing system was used to perform constant current charge-discharge tests on the assembled lithium-ion battery, setting different charge-discharge current densities and voltage ranges to obtain important parameters such as the initial charge-discharge capacity, coulombic efficiency, and cycle performance (number of cycles to 80% of the initial capacity) of the artificial graphite negative electrode material described in the examples or comparative examples. The results are shown in Table 2 below.

[0080] Table 2. Electrochemical performance test results of the artificial graphite anode materials described in the examples and comparative examples.

[0081] Initial discharge specific capacity (mAh / g) Initial efficiency (%) Cycle count Example 1 348.59 4.34 216 Example 2 349.29 4.44 279 Example 3 347.89 3.94 130 Example 4 347.29 3.84 025 Example 5 351.69 4.04 451 Comparative Example 1 344.49 3.03 453 Comparative Example 2 345.69 3.33 612 Comparative Example 3 346.79 3.53 551 surface

[0082] The theoretical discharge specific capacity of graphite is 372 mAh·g. -1 Therefore, for those skilled in the art, it is quite difficult to further improve the discharge specific capacity of graphite based on the existing technology. As can be seen from the data of Comparative Example 1 and Example 1 in Table 2, Example 2 improved the discharge specific capacity of graphite from 344.4 mAh·g simply by doping with nitrogen. -1 Increased to 348.5mAh·g -1 This improvement represents a significant technological advancement in the field.

[0083] Longer cycle life is also an urgent problem to be solved in battery development. In existing technologies, nitrogen doping is usually used to improve the electrochemical performance of batteries, but there are few reports of technologies that can significantly improve cycle life by simply doping artificial graphite with nitrogen.

[0084] As can be seen from the data in Table 2, compared with Example 1, when the nitrogen-free artificial graphite anode material prepared in Comparative Example 1 is applied to lithium-ion batteries, its various chemical properties, especially the number of cycles, decrease significantly.

[0085] Compared to Example 1, the order of nitrogen source addition in Comparative Example 2 was changed, with the nitrogen source added before graphitization. Since the graphitization temperature is as high as 3000°C, nitrogen will be lost in large quantities at high temperatures. Therefore, the artificial graphite material obtained in Comparative Example 2 retains only a small amount of nitrogen. When this graphite material is applied to lithium-ion batteries, the various electrochemical performances it exhibits are inferior to those in Example 1.

[0086] Compared to Example 1, the artificial graphite in Comparative Example 3 was not calcined with the nitrogen source under alkaline conditions. Although the nitrogen content of the artificial graphite material in Comparative Example 3 was not significantly different from that in Example 1, most of the nitrogen elements were not incorporated into the interior of the artificial graphite but concentrated on the graphite surface. Therefore, when lithium ions were inserted and extracted, the stress generated by the volume change was also concentrated on the graphite surface, which damaged the structure of the artificial graphite material. Ultimately, when the artificial graphite material of Comparative Example 3 was applied to a lithium-ion battery, its discharge specific capacity, initial efficiency, and cycle performance were all inferior to those of Example 1.

[0087] In summary, this invention utilizes a unique doping method to create a conductive network between the nitrogen atoms doped inside and outside the graphite and the graphite itself. This effectively reduces the damage to the graphite structure caused by lithium ions during insertion and extraction, thereby improving the cycle performance of lithium-ion batteries.

[0088] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-doped artificial graphite anode material, characterized in that, The process includes the following steps: S1, graphitizing the raw material coke to obtain artificial graphite; S2, combining the artificial graphite with a nitrogen source under alkaline conditions, and calcining the resulting material to obtain the negative electrode material. In step S2, the nitrogen source is at least one of polyvinylpyrrolidone or 2-methylimidazole; In step S2, prior to the composite process, the method further includes: performing a substitution condensation reaction between artificial graphite and chloroacetic acid to obtain carboxylated artificial graphite; in step S2, the composite process specifically includes: mixing artificial graphite, a nitrogen source, and an alkaline solution to form a paste; the pH of the alkaline solution is 9-10, specifically a KOH or NaOH solution; in step S2, the calcination temperature is 700-900℃.

2. The method for preparing nitrogen-doped artificial graphite anode material according to claim 1, characterized in that, In step S1, the raw material coke is at least one of needle coke, sponge coke, or petroleum coke.

3. The method for preparing nitrogen-doped artificial graphite anode material according to claim 1 or 2, characterized in that, In step S1, before the graphitization of the raw coke, the process further includes granulating the raw coke with a binder; the binder is at least one of petroleum asphalt, natural asphalt, or coal tar pitch; and the amount of binder used accounts for 8-12% of the mass of the raw coke.

4. The method for preparing nitrogen-doped artificial graphite anode material according to claim 1 or 2, characterized in that, In step S1, the graphitization temperature is 2800-3200℃; the D50 particle size of the artificial graphite is 15-17μm.

5. The method for preparing nitrogen-doped artificial graphite anode material according to claim 1 or 2, characterized in that, In step S2, the calcination is carried out under inert gas conditions.

6. A nitrogen-doped artificial graphite anode material, characterized in that, It is obtained by the preparation method described in any one of claims 1-5.

7. A lithium-ion battery, characterized in that, It includes the nitrogen-doped artificial graphite anode material as described in claim 6.

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