Asphalt-based hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses an asphalt-based hard carbon negative electrode material and a preparation method thereof, and the preparation method comprises the following steps: mixing asphalt and a cross-linking agent, carrying out high-pressure low-temperature pre-oxidation, adding an obtained hard carbon precursor into ZIF-8, uniformly mixing to form a coating layer, adding untreated asphalt, and finally carrying out high-temperature carbonization, crushing the powder to obtain a hard carbon material doped with nitrogen and zinc and coated with a layer of soft carbon; asphalt molecule cross-linking modification promotes an asphalt microstructure to be converted into hard carbon from soft carbon, and the pore structure of the material is regulated and controlled; heteroatom nitrogen and zinc doping improves sodium storage active sites and defect degree, and regulates and controls hard carbon layer spacing. And the closed-pore structure is adjusted through soft carbon coating, so that the low-potential sodium storage capacity is enhanced. Under the synergistic effect of three mechanisms of molecular cross-linking modification, heteroatom nitrogen and zinc doping and soft carbon coating, the novel asphalt-based hard carbon is far higher than traditional asphalt-based hard carbon in capacity and conductivity, and the novel asphalt-based hard carbon is simple to prepare and can be produced in a large scale.

Description

Technical Field

[0001] This invention belongs to the field of sodium electrode hard carbon technology, specifically a pitch-based hard carbon anode material and its preparation method. Background Technology

[0002] In recent years, lithium-ion batteries have been applied to large-scale energy storage and the development of electric vehicles. However, the total amount of lithium resources is limited and mostly located overseas, leading to significant price fluctuations in China. Sodium has similar physicochemical properties to lithium, and sodium-ion batteries use widely distributed and inexpensive raw materials. Sodium-ion batteries offer high safety and excellent low-temperature performance, meeting the requirements of high safety and low cost in the new energy field, and can serve as an effective supplement to lithium-ion batteries in certain areas.

[0003] As a key component of sodium-ion batteries, the cost and performance of anode materials directly determine the overall performance and market competitiveness of the battery. Therefore, developing low-cost, high-performance anode materials for sodium-ion batteries has become a research hotspot in the industry. Currently, biomass hard carbon materials suffer from limited production volume and difficulty in ensuring consistency between different batches, making it difficult to meet the demands of large-scale production. Asphalt, a byproduct of coal coking and petroleum distillation, is widely available and inexpensive, making it an ideal raw material for preparing hard carbon anode materials and possessing the potential for large-scale production. However, direct pyrolysis of asphalt easily generates graphitized soft carbon, which has poor sodium storage performance. Therefore, modification treatment is needed to prepare high-capacity hard carbon materials, thus requiring an efficient asphalt-based hard carbon modification and preparation technology. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems in the prior art and provide a pitch-based hard carbon anode material with synergistic effects of three mechanisms and its preparation method. Through the synergistic regulation of pitch molecule crosslinking modification, heteroatomic nitrogen-zinc doping, and soft carbon coating, the invention addresses the problems of unreasonable pore structure, insufficient sodium storage active sites, and weak low-potential sodium storage capacity in traditional pitch-based hard carbon materials. This results in a hard carbon anode material with low porosity, large interlayer spacing, high capacity, and high conductivity, while simplifying the preparation process, reducing production costs, and meeting the needs of large-scale production. The specific technical solution is as follows: A method for preparing pitch-based hard carbon anode material, through the synergistic effect of a triple mechanism of high-pressure pre-oxidation crosslinking, ZIF-8 nitrogen-zinc co-doping, and secondary pitch soft carbon coating, specifically includes the following steps: S1: Mix 20 wt.%-45 wt.% crosslinking agent, 5 wt.%-15 wt.% KOH with asphalt by mechanical stirring at room temperature for 30-60 minutes until homogeneous, and then form into blocks by applying a pressure of 3-7 MPa; S2: The prepared block mixture is heated to 200℃-300℃ in air at a heating rate of 5-10℃ / min, and kept at a pressure of 0.2-0.5Mpa for 2-6 hours to carry out high-pressure pre-oxidation treatment, which promotes the cross-linking of asphalt molecules and inhibits graphitization in the subsequent carbonization process. S3: Immerse the pre-oxidized product under high pressure in 0.5-2 mol / L acid solution for 2-4 hours to remove impurities, wash with deionized water until neutral pH=6.5-7.5, and dry at 80-120℃ for 6-12 hours; S4: Add deionized water and finished ZIF-8 to the high-pressure pre-oxidized product, and ultrasonically disperse for 20-30 minutes to obtain a homogeneous mixed liquid. Control the mass ratio of ZIF-8 to 1.5wt.%-5wt.%. S5: After filtering the mixed liquid, dry it at 80-120℃ for 12-24h, mechanically stir for 20-30min to mix it evenly, raise the temperature to 900℃-1400℃ at a heating rate of 10-20℃ / min under an inert gas atmosphere, and keep it at the temperature for 3-6h under normal pressure. The asphalt powder forms a soft carbon coating layer during the calcination process. Finally, crush the material and pass it through a mesh sieve to obtain the composite hard carbon material.

[0005] Preferably, the crosslinking agent in S1 is selected from ammonium acetate, ammonium carbonate, ammonium nitrate, ethylenediamine, triethylenetetramine, and polyethyleneimine; the amount of crosslinking agent added is 30 wt.%-40 wt.%, the amount of KOH added is 8 wt.%-12 wt.%, and the pressing pressure is 4-6 MPa. This ratio increases the crosslinking density of asphalt molecules by 30%-40% and reduces the degree of graphitization to below 15%.

[0006] Preferably, the acid solution in S3 is selected from dilute hydrochloric acid, dilute sulfuric acid, or phosphoric acid; the acid concentration is 0.8-1.5 mol / L, and the soaking time is 2.5-3.5 h. This method can efficiently remove inorganic impurities generated during the pre-oxidation process without damaging the carbon skeleton structure.

[0007] Preferably, in S4, ZIF-8 is used as both a nitrogen and zinc source to introduce nitrogen and zinc doping sites into the carbon framework; the mass ratio of ZIF-8 is 2 wt.%-4 wt.%, the particle size is 80-150 nm, the nitrogen doping amount reaches 2.5-4.0 at.%, and the zinc doping amount reaches 0.5-1.2 at.%; the number of sodium storage active sites is increased by more than 50%.

[0008] Preferably, the gas in S5 is selected from nitrogen, helium, or argon, and the amount of asphalt powder added is 5wt.%-10wt.%. After crushing, it is passed through a 200-400 mesh sieve, and the particle size of the resulting composite hard carbon material is 5-15μm. This ratio increases the conductivity of the material to 100-150S / m, and the low-potential sodium storage capacity accounts for ≥60%.

[0009] A pitch-based hard carbon anode material, wherein the material has a nitrogen-zinc co-doped structure, a surface coated with a 5-20 nm thick soft carbon layer, and a carbon layer spacing of 0.37-0.39 nm, a Raman D peak to G peak intensity ratio ID / IG of 1.8-2.5, a sodium storage capacity ≥310 mAh / g, and an initial coulombic efficiency ≥89%.

[0010] Compared with the closest existing technology, the technical solution provided by the present invention has the following beneficial effects: 1. This invention constructs a synergistic system by combining high-pressure pre-oxidation crosslinking, ZIF-8 nitrogen-zinc co-doping, and secondary asphalt soft carbon coating, rather than a simple superposition of a single mechanism. The asphalt is first crosslinked and hybridized, then subjected to a high-pressure pre-oxidation process, followed by acid washing to neutralize the acidity and alkalinity, then mixed with ZIF-8 for heterogeneous element doping, and finally coated with asphalt and fired at high temperature to obtain composite hard carbon. Compared with conventional asphalt-based materials, it has higher capacity and rate performance, with a capacity increase of 6%-28% and an initial coulombic efficiency of 89.7%-91.5%.

[0011] 2. This invention regulates the microstructure of pitch-based hard carbon by adding a crosslinking agent, transforming pitch from soft carbon to hard carbon and regulating the pore structure of the material; the ZIF-8 coating achieves the purpose of heteroatomic nitrogen and zinc doping, improving the active sites and defect degree of sodium storage, and regulating the interlayer spacing of hard carbon; the soft carbon coating regulates the closed-pore structure, thereby enhancing the sodium storage capacity at low potentials and improving the electrochemical sodium storage performance, with a sodium storage capacity of up to 315-346 mAh / g.

[0012] 3. The preparation process of this invention does not require complex equipment, the steps are controllable, and the key parameter ranges are clearly defined, making it suitable for continuous industrial production. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the process principle of the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1 A method for preparing pitch-based hard carbon anode material, through the synergistic effect of a triple mechanism of high-pressure pre-oxidation crosslinking, ZIF-8 nitrogen-zinc co-doping, and secondary pitch soft carbon coating, specifically includes the following steps: S1: Mix 25 wt.% ammonium carbonate, 5 wt.% KOH and asphalt to obtain a mixture, and then press it into blocks under a pressure of 3 MPa; S2: The prepared block mixture is heated in air at 200℃ and 0.2Mpa for 4h; high-pressure pre-oxidation treatment is carried out to promote cross-linking of asphalt molecules and inhibit graphitization in the subsequent carbonization process; S3: Immerse the pre-oxidized product under high pressure in 1.0 mol / L dilute sulfuric acid, wash with deionized water until neutral, and dry. S4: Add deionized water and finished ZIF-8 to the high-pressure pre-oxidized product and mix thoroughly to obtain a mixed liquid, controlling the mass ratio of ZIF-8 to 1.5 wt.%; S5: After filtering and drying the above mixed liquid for 12 hours, 2 wt.% of asphalt powder is added and mixed evenly. The mixture is then calcined at 900°C and normal pressure for 3 hours under a nitrogen atmosphere. During the calcination process, the asphalt powder forms a soft carbon coating layer. Finally, the material is crushed and sieved to obtain a composite hard carbon material.

[0016] Example 2 A method for preparing pitch-based hard carbon anode material, through the synergistic effect of a triple mechanism of high-pressure pre-oxidation crosslinking, ZIF-8 nitrogen-zinc co-doping, and secondary pitch soft carbon coating, specifically includes the following steps: S1: Mix 35 wt.% ammonium acetate, 10 wt.% KOH and asphalt to obtain a mixture, and then press it into blocks under a pressure of 4 MPa; S2: The prepared block mixture is heated in air at 300℃ and 0.4Mpa for 6 hours; high-pressure pre-oxidation treatment is carried out to promote cross-linking of asphalt molecules and inhibit graphitization in the subsequent carbonization process; S3: Immerse the pre-oxidized product under high pressure in 1.0 mol / L dilute hydrochloric acid, wash with deionized water until neutral, and dry. S4: Add deionized water and finished ZIF-8 to the high-pressure pre-oxidized product and mix thoroughly to obtain a mixed liquid, controlling the mass ratio of ZIF-8 to 3 wt.%; S5: After filtering and drying the above mixed liquid for 16 hours, 8 wt.% of asphalt powder is added and mixed evenly. The mixture is then calcined at 1200°C and normal pressure for 4 hours under a nitrogen atmosphere. During the calcination process, the asphalt powder forms a soft carbon coating layer. Finally, the material is crushed and sieved to obtain a composite hard carbon material.

[0017] Example 3 A method for preparing pitch-based hard carbon anode material, through the synergistic effect of a triple mechanism of high-pressure pre-oxidation crosslinking, ZIF-8 nitrogen-zinc co-doping, and secondary pitch soft carbon coating, specifically includes the following steps: S1: Mix 45 wt.% ammonium nitrate, 15 wt.% KOH and asphalt to obtain a mixture, and then press it into blocks under a pressure of 5 MPa; S2: The prepared block mixture is heated in air at 300℃ and 0.5Mpa for 5h; high-pressure pre-oxidation treatment is carried out to promote cross-linking of asphalt molecules and inhibit graphitization in the subsequent carbonization process; S3: Immerse the pre-oxidized product under high pressure in 1.0 mol / L acid solution, wash with deionized water until neutral, and dry. S4: Add deionized water and finished ZIF-8 to the high-pressure pre-oxidized product and mix thoroughly to obtain a mixed liquid, controlling the mass ratio of ZIF-8 to 5 wt.%; S5: After filtering and drying the above mixed liquid for 18 hours, 14 wt.% of asphalt powder is added and mixed evenly. The mixture is then calcined at 1400℃ and normal pressure for 6 hours under a nitrogen atmosphere. During the calcination process, the asphalt powder forms a soft carbon coating layer. Finally, the material is crushed and sieved to obtain a composite hard carbon material.

[0018] Comparative Example 1 Hard carbon materials were prepared according to the method of Example 2, except that step 1, in which 35 wt.% ammonium nitrate, 10 wt.% KOH and pitch were mixed, was omitted.

[0019] Comparative Example 2 Hard carbon materials were prepared according to the method in Example 2, except that step 4, adding deionized water and finished ZIF-8 and mixing them evenly, was omitted, and the mass ratio of ZIF-8 was controlled to be 3 wt.%.

[0020] Comparative Example 3 Hard carbon materials were prepared according to the method of Example 2, except that step 5, which involves adding 8 wt.% asphalt powder, was omitted.

[0021] The performance of the sodium-ion battery anode materials prepared according to Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in the table below: Table 1 Test data of Examples 1-3 and Comparative Examples 1-3 As can be seen from the test data in Table 1, the sodium-ion battery anode material prepared using the method of this invention exhibits a significantly improved capacity and good initial coulombic efficiency. The conductivity of the hard carbon coated with soft carbon is also enhanced.

[0022] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing pitch-based hard carbon anode material, characterized in that, The process involves a synergistic effect of three mechanisms: high-pressure pre-oxidation crosslinking, ZIF-8 nitrogen-zinc co-doping, and secondary pitch soft carbon coating. Specifically, the steps include: S1: Mix 20 wt.%-45 wt.% crosslinking agent, 5 wt.%-15 wt.% KOH with asphalt by mechanical stirring at room temperature for 30-60 minutes until homogeneous, and then form into blocks by applying pressure of 3-7 MPa; S2: The prepared block mixture is heated to 200℃-300℃ in air at a heating rate of 5-10℃ / min, and kept at a pressure of 0.2-0.5Mpa for 2-6 hours to carry out high-pressure pre-oxidation treatment, which promotes the cross-linking of asphalt molecules and inhibits graphitization in the subsequent carbonization process. S3: Immerse the pre-oxidized product under high pressure in 0.5-2 mol / L acid solution for 2-4 hours to remove impurities, wash with deionized water until neutral pH=6.5-7.5, and dry at 80-120℃ for 6-12 hours; S4: Add deionized water and finished ZIF-8 to the high-pressure pre-oxidized product, and ultrasonically disperse for 20-30 minutes to obtain a homogeneous mixed liquid. Control the mass ratio of ZIF-8 to 1.5wt.%-5wt.%. S5: After filtering the mixed liquid, dry it at 80-120℃ for 12-24h, mechanically stir for 20-30min to mix it evenly, raise the temperature to 900℃-1400℃ at a heating rate of 10-20℃ / min under an inert gas atmosphere, and keep it at the temperature for 3-6h under normal pressure. The asphalt powder forms a soft carbon coating layer during the calcination process. Finally, crush the material and pass it through a mesh sieve to obtain the composite hard carbon material.

2. The method for preparing pitch-based hard carbon anode material according to claim 1, characterized in that, The crosslinking agent in S1 can be selected from ammonium acetate, ammonium carbonate, ammonium nitrate, ethylenediamine, triethylenetetramine, or polyethyleneimine; the amount of crosslinking agent added is 30 wt.%-40 wt.%, the amount of KOH added is 8 wt.%-12 wt.%, and the pressing pressure is 4-6 MPa.

3. The method for preparing pitch-based hard carbon anode material according to claim 1, characterized in that, The acid solution in S3 can be any one of dilute hydrochloric acid, dilute sulfuric acid, or phosphoric acid; the acid concentration is 0.8-1.5 mol / L, and the soaking time is 2.5-3.5 h.

4. The method for preparing pitch-based hard carbon anode material according to claim 1, characterized in that, In S4, ZIF-8 serves as both a nitrogen and zinc source, used to introduce nitrogen and zinc doping sites into the carbon framework. The mass ratio of ZIF-8 is 2 wt.%-4 wt.%, the particle size is 80-150 nm, and the nitrogen doping amount reaches 2.5-4.0 at.% and the zinc doping amount reaches 0.5-1.2 at.%.

5. The method for preparing pitch-based hard carbon anode material according to claim 1, characterized in that, The gas in S5 can be any one of nitrogen, helium, or argon. The amount of asphalt powder added is 5wt.%-10wt.%. After crushing, it is passed through a 200-400 mesh sieve, and the particle size of the resulting composite hard carbon material is 5-15μm.

6. A pitch-based hard carbon anode material, characterized in that, The material is prepared by the method described in any one of claims 1 to 4, and has a nitrogen-zinc co-doped structure, a soft carbon layer with a thickness of 5-20 nm on the surface, a carbon layer spacing of 0.37-0.39 nm, a Raman D peak to G peak intensity ratio ID / IG of 1.8-2.5, a sodium storage capacity ≥310 mAh / g, and an initial coulombic efficiency ≥89%.

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