A method for preparing a high-capacity pitch-based hard carbon sodium ion battery negative electrode material

Abstract

The present invention discloses a method for preparing a high-capacity asphalt-based hard carbon negative electrode material for sodium ion batteries. The asphalt-based hard carbon material is prepared by adopting a combined pre-oxidation-precarbonization process and a zinc salt catalysis method. The present invention further pre-carbonizes the pre-oxidized asphalt raw material to reduce surface defects of the final hard carbon product, thereby improving the initial efficiency and capacity of the sodium ion battery. The preparation method is simple, the process is controllable, the cost is low, and it is easy to promote and implement industrially.

Description

Technical Field

[0001] The present application belongs to the field of sodium battery technology and relates to a method for preparing a high-capacity asphalt-based hard carbon sodium ion battery negative electrode material. Background Art

[0002] Compared with lithium, sodium has huge reserves in the earth's crust, is widely distributed around the world, and is low in cost. Therefore, sodium-ion batteries have more advantages in large-scale energy storage devices.

[0003] Sodium-ion batteries are low-cost, high-performance, and environmentally friendly secondary batteries with similar working principles to lithium-ion batteries. However, the radius of sodium ions (0.102nm, more than 40% larger than lithium ions) is larger, making it difficult to directly use traditional graphite negative electrode materials to complete the process of sodium ion extraction and insertion. Amorphous hard carbon materials are considered to be the most promising negative electrode materials for the industrialization of sodium ions because they have larger interlayer spacing (>0.34nm), more complex microcrystalline structures (arranged in a random orientation), and more abundant sodium storage sites (sodium storage locations include between graphite sheets, closed micropores, surfaces, and defect sites).

[0004] Pitch, with its low cost, abundant resources, and high carbon content, is one of the most promising hard carbon precursors. While hard carbon materials can be produced through simple pre-oxidation treatments, their specific capacity and initial efficiency are often unsatisfactory. Therefore, the development of hard carbon anode materials with high capacity, high initial efficiency, and excellent cycling performance using low-cost, easily scalable methods is a crucial step toward the industrialization of sodium-ion batteries. Summary of the Invention

[0005] The present invention aims to solve the technical problems existing in the existing technology of asphalt-based hard carbon, and proposes a preparation method for a high-capacity asphalt-based hard carbon sodium ion battery negative electrode material. The asphalt-based hard carbon material is prepared by adopting a pre-oxidation-precarbonization combined treatment and a zinc salt catalysis method. The present invention uses the asphalt raw material after pre-oxidation to further precarbonize the process to reduce the surface defects of the final hard carbon product and improve the initial efficiency and capacity of the sodium ion battery. The preparation method is simple, the process is controllable, the cost is low, and it is easy to promote and implement industrialization.

[0006] The technical solutions adopted in the present invention are as follows:

[0007] A method for preparing a high-capacity pitch-based hard carbon sodium ion battery negative electrode material is carried out in the following steps in sequence:

[0008] S1. Complete the pre-oxidation process of the asphalt in an oxidizing atmosphere, switch the gas source to inert gas, and heat it to 550-650℃ to complete the pre-carbonization process;

[0009] S2. Grinding the intermediate product after pre-carbonization to obtain intermediate product powder;

[0010] S3. uniformly mixing the intermediate product powder with the zinc salt to obtain a hard carbon precursor mixture containing the zinc salt;

[0011] S4. Put the mixed material into a high-temperature carbonization furnace, raise the temperature to 1000-1800°C under an inert atmosphere and carbonize and keep the temperature for 2-10 hours;

[0012] S5. Cooling the product after high-temperature carbonization treatment to room temperature to obtain a sodium ion battery negative electrode material.

[0013] The present invention creatively adopts a pre-oxidation-pre-carbonization process to treat asphalt. During the pre-oxidation process, oxidative cross-linking occurs to form a pre-oxide containing a large number of oxygen-containing groups. During the pre-carbonization process, rearrangement and departure of carbon-oxygen functional groups occur to obtain a relatively stable carbon-oxygen network structure. Compared with the formal conventional carbonization process, the pre-carbonization process of the present application can improve the stability of the pre-oxide structure itself, reduce the agglomeration of particles during the pyrolysis process, and obtain uniform, stable hard carbon particles with excellent electrochemical properties.

[0014] As a limitation of the present invention, in step S1, the asphalt is one or more of natural asphalt, petroleum asphalt, coal tar asphalt, shale oil asphalt, bio-asphalt, and naphthalene asphalt.

[0015] During the pyrolysis process of asphalt, the volatilization and gasification phase generally occurs below 650°C. Pre-carbonization after pre-oxidation can rearrange or dissociate carbon-oxygen groups, minimizing the damage caused by the pyrolysis phase to the carbon-oxygen skeleton structure formed during the pre-oxidation phase. This treatment also reduces the number of highly reactive groups on the surface of the asphalt molecules, reducing the adhesion and agglomeration of hard carbon particles in the asphalt. Therefore, during the subsequent secondary heating process, asphalt treated in this way will maintain a better internal group structure, resulting in hard carbon particles with fewer defects.

[0016] As a second limitation of the present invention, in step S1, the heating rate of the pre-oxidation is 0.5-5°C / min, the pre-oxidation temperature is 250-350°C, and the heating rate of the pre-carbonization is 1-10°C / min;

[0017] As a third limitation of the present invention, in step S3, the zinc salt is one or more of EDTA zinc salt, zinc gluconate, zinc adipate, zinc phenylacetate, zinc acetate, zinc succinate, zinc chloride, zinc sulfate, zinc nitrate, zinc phosphate, zinc sulfide, and zinc oxide.

[0018] As a fourth limitation of the present invention, in step S3, the mass ratio of the precursor to the zinc salt is (1-5):1.

[0019] The present invention mixes the asphalt precursor after pre-oxidation and pre-carbonization with zinc salt in a certain proportion and completes the carbonization process in an inert or reducing atmosphere. During this process, the zinc salt provided by the present invention can regulate the carbon-oxygen structure inside the asphalt, promote the rearrangement and fixation of carbon substances and the departure of oxygen atoms during pyrolysis, and finally volatilize and detach in the form of zinc vapor, avoiding the increase of ash content. This process can effectively increase the crystallite disorder of hard carbon, increase the interlayer spacing of carbon materials, and maintain smaller surface defects while ensuring the acquisition of more sodium storage sites.

[0020] As a fifth limitation of the present invention, in step S1 and step S4, the gas of the inert atmosphere is one or more of Ar, He, N2, and H2.

[0021] The present invention has another limitation, that in step S4, the heating rate of the carbonization is 0.5-20°C / min.

[0022] In the present invention, the heating rate of the high-temperature carbonization in step S4 is relatively important, which affects the number of defects in the hard carbon product. When the heating rate exceeds 20°C / min, the hard carbon will produce more defects, seriously reducing the initial efficiency and cycle stability of the hard carbon material. When the heating rate is less than 0.5°C / min, it will cause excessive energy consumption, leading to an increase in production costs.

[0023] The preparation method described above, as a whole, is organically interconnected, with each step integrally linked. Using low-cost asphalt as a precursor and an organic or inorganic zinc salt as a pyrolysis catalyst, the method improves upon a one-step pre-oxidation process to produce a sodium-ion battery negative electrode material with high initial efficiency and sodium storage capacity. The method also features a simple production process, highly controllable carbonization process, low production cost, and high carbon yield, enabling large-scale production.

[0024] By adopting the above technical solution, the beneficial effects achieved by this application are as follows:

[0025] 1. The present invention further pre-carbonizes the pre-oxidized asphalt raw material to reduce surface defects of the final hard carbon product and improve the initial efficiency and capacity of the sodium ion battery.

[0026] 2. The preparation method is simple, the process is controllable, the cost is low, and it is easy to promote and implement industrialization.

[0027] 3. The hard carbon material has good electrochemical performance as the negative electrode material of sodium ion batteries. The reversible capacity reaches 374.91 mAh / g at a current density of 30 mA / g, and the first coulombic efficiency reaches 83.82%.

[0028] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an SEM image of the pitch hard carbon material prepared in Example 1;

[0030] Figure 2 This is the XRD pattern of the pitch hard carbon material prepared in Example 1;

[0031] Figure 3 This is a pore size distribution diagram of the pitch hard carbon material prepared in Example 1;

[0032] Figure 4 This is a test diagram of the electrochemical performance of the pitch hard carbon material prepared in Example 1. DETAILED DESCRIPTION

[0033] In the following examples, the reagents described are all commercially available unless otherwise specified, and the following experimental methods and detection methods are all based on existing experimental methods and detection methods unless otherwise specified.

[0034] Example 1

[0035] This example prepares a hard carbon negative electrode material for sodium ion batteries. The specific process is as follows:

[0036] (1) Using high-temperature petroleum asphalt as raw material, the temperature was raised to 300°C at a rate of 5°C / min in an O2 atmosphere and kept at this temperature for 3 hours to complete the pre-oxidation process. Then, the atmosphere was switched to Ar and the temperature was continued to be raised to 550°C at a rate of 2°C / min to complete the pre-carbonization process.

[0037] (2) crushing and mixing the pre-oxidized-pre-carbonized asphalt obtained in step (1) and zinc acetate in a mass ratio of 1:1 to obtain a mixture containing zinc salt;

[0038] (3) The mixture in step (2) was placed in a tube furnace, and under the protection of Ar, the temperature was raised to 1400°C at a heating rate of 10°C / min, kept at this temperature for 2 hours, and cooled to room temperature to prepare a high-performance sodium ion battery negative electrode hard carbon material. A series of characterization results of the prepared material are as follows:

[0039] Figure 1 This is the SEM image of the hard carbon material, from which we can see that the surface of the hard carbon particles is relatively smooth, the particles are small, and there are no obvious pore defects.

[0040] Figure 2 This is the XRD diagram of the hard carbon material. It can be seen from the figure that the diffraction peak half-maximum width of the (002) crystal plane of the carbon material is large and the angle is small, indicating that the microcrystals of this hard carbon material are highly disordered and the interlayer spacing is large, which is conducive to the deintercalation of sodium ions.

[0041] Figure 3This is the pore size distribution diagram of the hard carbon material, from which it can be seen that the pore size in the material is mainly concentrated below 5nm.

[0042] Figure 4 The first and second charge and discharge curves of the battery when the obtained hard carbon material is used as the negative electrode of the sodium ion battery. It can be seen that the first efficiency of the negative electrode material is high and the cycle stability is good.

[0043] Example 2

[0044] (1) Using naphthalene pitch as raw material, the temperature was raised to 250°C at a rate of 3°C / min in an air atmosphere and kept at this temperature for 6 h to complete the pre-oxidation process. Then, the atmosphere was switched to N2 and the temperature was continued to be raised to 600°C at a rate of 5°C / min to complete the pre-carbonization process.

[0045] (2) crushing and mixing the pre-oxidized-pre-carbonized asphalt obtained in step (1) and zinc chloride in a mass ratio of 5:1 to obtain a mixture containing zinc salt;

[0046] (3) The mixture in step (2) is placed in a tubular furnace, and under the protection of N2, the temperature is increased to 1800°C at a heating rate of 5°C / min, kept at this temperature for 6 hours, and cooled to room temperature to obtain a high-performance sodium ion battery negative electrode hard carbon material.

[0047] Example 3

[0048] This example prepares a hard carbon negative electrode material for sodium ion batteries. The specific process is as follows:

[0049] (1) Using shale oil asphalt as raw material, the temperature was raised to 300°C at a rate of 0.5°C / min in an O2 atmosphere and kept at this temperature for 3 h to complete the pre-oxidation process. Then the atmosphere was switched to N2 and the temperature was continued to be raised to 650°C at a rate of 1°C / min to complete the pre-carbonization process.

[0050] (2) crushing and mixing the pre-oxidized-pre-carbonized asphalt obtained in step (1) and zinc gluconate in a mass ratio of 3:1 to obtain a mixture containing zinc salt;

[0051] (3) The mixture in step (2) is placed in a tubular furnace, and under the protection of N2, the temperature is increased to 1000°C at a heating rate of 20°C / min, kept warm for 10 hours, and cooled to room temperature to prepare a high-performance sodium ion battery negative electrode hard carbon material.

[0052] Example 4

[0053] This example prepares a hard carbon negative electrode material for sodium ion batteries. The specific process is as follows:

[0054] (1) Using bioasphalt as raw material, the temperature was raised to 350°C at a rate of 5°C / min in an O2 atmosphere and kept at this temperature for 3 h to complete the pre-oxidation process. Then, the atmosphere was switched to Ar and the temperature was continued to be raised to 550°C at a rate of 10°C / min to complete the pre-carbonization process.

[0055] (2) crushing and mixing the pre-oxidized-pre-carbonized asphalt obtained in step (1) and zinc nitrate in a mass ratio of 1:1 to obtain a mixture containing zinc salt;

[0056] (3) The mixture in step (2) is placed in a tubular furnace, and under the protection of Ar, the temperature is increased to 1400°C at a heating rate of 0.5°C / min, kept at this temperature for 4 hours, and cooled to room temperature to prepare a high-performance sodium ion battery negative electrode hard carbon material.

[0057] Example 5

[0058] This example prepares a hard carbon negative electrode material for sodium ion batteries. The specific process is as follows:

[0059] (1) Using high-temperature coal tar pitch as raw material, the temperature was raised to 300°C at a rate of 5°C / min in an air atmosphere and kept at this temperature for 6 hours to complete the pre-oxidation process. Then the atmosphere was switched to N2 and the temperature was continued to be raised to 550°C at a rate of 2°C / min to complete the pre-carbonization process.

[0060] (2) The pre-oxidized-pre-carbonized asphalt obtained in step (1) and EDTA zinc salt are crushed and mixed in a mass ratio of 1:1 to obtain a mixture containing zinc salt.

[0061] (3) The mixture in step (2) is placed in a tubular furnace, and under the protection of N2, the temperature is raised to 1400°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, and cooled to room temperature to prepare a high-performance sodium ion battery negative electrode hard carbon material.

[0062] Example 6

[0063] This example prepares a hard carbon negative electrode material for sodium ion batteries. The specific process is as follows:

[0064] (1) Using natural asphalt as raw material, the temperature was raised to 300°C at a rate of 5°C / min in an air atmosphere and kept at this temperature for 6 h to complete the pre-oxidation process. Then the atmosphere was switched to N2 and the temperature was continued to be raised to 550°C at a rate of 2°C / min to complete the pre-carbonization process.

[0065] (2) crushing and mixing the pre-oxidized and pre-carbonized asphalt obtained in step (1) and a mixed salt of zinc adipate and zinc succinate (the two zinc salts are mixed in a mass ratio of 1:1) in a mass ratio of 2:1 to obtain a mixture containing zinc salt;

[0066] (3) The mixture in step (2) is placed in a tubular furnace, and under the protection of N2, the temperature is increased to 1400°C at a heating rate of 10°C / min, kept warm for 2 hours, and cooled to room temperature to prepare a high-performance sodium ion battery negative electrode hard carbon material.

[0067] Comparative Example 1

[0068] In this comparative example, a hard carbon material for a negative electrode of a sodium ion battery is prepared. The preparation process is the same as that of Example 1 except that no zinc salt is mixed.

[0069] Comparative Example 2

[0070] In this comparative example, a hard carbon material for a negative electrode of a sodium ion battery was prepared. The preparation process was the same as in Example 1 except that the pre-oxidation-pre-carbonization combined treatment was not performed.

[0071] Comparative Example 3

[0072] In this comparative example, a hard carbon material for a negative electrode of a sodium ion battery was prepared. The preparation process was the same as in Example 1, except that no zinc salt was mixed and no pre-oxidation-pre-carbonization combined treatment was performed.

[0073] Comparative Example 4

[0074] In this comparative example, a hard carbon material for the negative electrode of a sodium ion battery was prepared. Only a pre-oxidation treatment was performed without a pre-carbonization treatment and without mixing any zinc salt. The other steps were the same as those in Example 1.

[0075] Comparative Example 5

[0076] In this comparative example, a hard carbon material for the negative electrode of a sodium ion battery was prepared. Only a pre-oxidation treatment was performed without a pre-carbonization treatment. The other steps were the same as those in Example 1.

[0077] Comparative Example 6

[0078] In this comparative example, a hard carbon material for the negative electrode of a sodium ion battery was prepared. Only a pre-carbonization treatment was performed without a pre-oxidation treatment. The other steps were the same as those in Example 1.

[0079] The present invention assembles a sodium ion battery using the negative electrode materials obtained in the above examples and comparative examples and performs electrochemical performance tests on the battery.

[0080] Preparation of half-cell: The negative electrode asphalt-based hard carbon material obtained in the embodiment and comparative example was mixed with the conductive agent SP and the binder sodium alginate (SA) in an active mass percentage ratio of 85:5:10 to prepare a test electrode. Metallic sodium was used as the counter electrode, Whatman GF / D glass fiber was used as the diaphragm, and the electrolyte was ethylene carbonate (EC) / dimethyl carbonate (DMC) solution (solvent volume ratio 1:1) with 1M NaPF6 as the electrolyte salt. The battery was assembled in an argon-filled glove box.

[0081] After the battery is assembled, it is left to stand for 12 hours and then subjected to charge and discharge tests. The voltage window is 0.01-2V, and the charge and discharge tests are completed at a current density of 30mA / g.

[0082] The specific test results are shown in Table 1 below.

[0083] Table 1 Test results

[0084]

[0085]

[0086] Through the test results of Example 1 and Comparative Example 1, it can be found that the addition of zinc salt can significantly improve the sodium storage capacity of asphalt-based hard carbon. This is because the zinc salt regulates the internal pore structure of asphalt-based hard carbon during the pyrolysis process, promotes the rearrangement and fixation of carbon matter during the pyrolysis process, retains a larger interlayer spacing, and makes the asphalt-based hard carbon have more micropores and closed-pore structures and small surface defects, while improving the sodium storage capacity and first effect.

[0087] The test results of Comparative Examples 3 and 4 indicate that the combined pre-oxidation treatment strategy can enhance the sodium storage capacity of asphalt-based hard carbon. This is due to the introduction of a large number of oxygen-containing functional groups during the pre-oxidation process. These functional groups cross-link the asphalt molecules to form a spatial network structure, thereby restricting their movement. This macroscopically manifests as a continuously increasing softening point, ultimately resulting in a fully solidified hard carbon precursor with improved sodium storage performance. However, the introduction of a large number of oxygen-containing functional groups during the pre-oxidation process makes the asphalt hard carbon particles more likely to adhere and agglomerate, resulting in larger final hard carbon particles.

[0088] The test results of Example 1, Comparative Example 2, and Comparative Example 6 indicate that adding a pre-carbonization step after pre-oxidation—that is, a combined pre-oxidation-pre-carbonization process—can effectively improve the sodium storage performance of asphalt hard carbon. This is because the pre-carbonization process rearranges or dissociates carbon-oxygen groups, reducing the damage to the newly formed internal carbon-oxygen skeleton during the pyrolysis stage. Simultaneously, this treatment reduces the highly reactive groups on the surface of the asphalt molecules, reducing the adhesion and agglomeration of asphalt hard carbon particles later in the process. Therefore, asphalt treated using this method maintains a well-defined internal group structure, resulting in hard carbon particles with fewer defects.

[0089] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high-capacity pitch-based hard carbon sodium ion battery negative electrode material, characterized in that: Follow the steps below in order: S1. Complete the pre-oxidation process of the asphalt in an oxidizing atmosphere, switch the gas source to inert gas, and heat it to 550-650℃ to complete the pre-carbonization process; The heating rate of the pre-oxidation is 0.5-5°C / min, the pre-oxidation temperature is 250-350°C, and the heating rate of the pre-carbonization is 1-10°C / min; S2. Grinding the intermediate product after pre-carbonization to obtain intermediate product powder; S3. uniformly mixing the intermediate product powder and the zinc salt, wherein the mass ratio of the intermediate product powder to the zinc salt is (1-5):1, to obtain a hard carbon precursor mixture containing the zinc salt; S4. Put the mixed material into a high-temperature carbonization furnace, raise the temperature to 1000-1800°C under an inert atmosphere and carbonize and keep the temperature for 2-10 hours; S5. Cooling the product after high-temperature carbonization treatment to room temperature to obtain a sodium ion battery negative electrode material.

2. The method for preparing a high-capacity pitch-based hard carbon sodium ion battery negative electrode material according to claim 1, characterized in that: In step S1, the asphalt is one or more of natural asphalt, petroleum asphalt, coal tar asphalt, shale oil asphalt, bio-asphalt, and naphthalene asphalt.

3. The method for preparing a high-capacity pitch-based hard carbon sodium ion battery negative electrode material according to claim 1, characterized in that: In step S3, the zinc salt is one or more of EDTA zinc salt, zinc gluconate, zinc adipate, zinc phenylacetate, zinc acetate, zinc succinate, zinc chloride, zinc sulfate, zinc nitrate, zinc phosphate, and zinc sulfide.

4. The method for preparing a high-capacity pitch-based hard carbon sodium ion battery negative electrode material according to claim 1, characterized in that: In step S1 and step S4, the gas of the inert atmosphere is one or more of Ar, He, N2, and H2.

5. The method for preparing a high-capacity pitch-based hard carbon sodium ion battery negative electrode material according to claim 1, characterized in that: In step S4, the carbonization heating rate is 0.5-20°C / min.

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