A hard carbon material, a preparation method and application thereof

Abstract

The application provides a hard carbon material and a preparation method and application thereof, relates to the technical field of sodium ion batteries, and the preparation method of the hard carbon material comprises the following steps: S1, mixing wood tar and acetic acid according to a preset mass ratio, and stirring at a preset temperature to obtain a mixture; S2, performing high-temperature carbonization on the mixture in a protective gas atmosphere to obtain the hard carbon material. The hard carbon material prepared by the method has high initial coulomb efficiency and good cycle performance. The hard carbon material is used for preparing a sodium ion battery, and the initial coulomb efficiency and cycle stability of the sodium ion battery can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a hard carbon material, its preparation method, and its application. Background Technology

[0002] Amidst the energy transition, sodium-ion batteries, with their significant advantages such as abundant and widely distributed sodium resources and low cost, have become a promising new electrochemical energy storage technology in the energy storage and low-speed transportation sectors, potentially alleviating the industrial pressure caused by the supply and demand imbalance of lithium resources. The anode material, as a core component of sodium-ion batteries, directly determines the battery's energy density, cycle life, and charge-discharge performance. Traditional graphite anodes, due to their small interlayer spacing, are difficult to adapt to the large ionic radius of sodium ions, hindering the effective insertion and extraction of sodium ions and failing to meet the performance requirements of sodium-ion batteries.

[0003] Hard carbon materials, due to their unique disordered layer structure, large interlayer spacing, and abundant nanopore system, can provide ample insertion sites and rapid transport channels for sodium ions, making them one of the most promising anode materials for sodium-ion batteries. Currently, the raw materials for hard carbon material preparation are widely available, mainly including thermosetting resins and polymers. Wood tar, a major byproduct of wood pyrolysis, has a huge annual output, but its complex composition, rich in phenols, aromatic hydrocarbons, heterocyclic compounds, and other carbonaceous components, has long been used as a low-value fuel for incineration, failing to achieve high-value utilization. In fact, the abundant aromatic carbon skeleton in wood tar provides a high-quality carbon source for hard carbon material preparation, possessing extremely high carbonization potential and representing a low-cost hard carbon precursor with significant development value. However, currently, hard carbon materials prepared from wood tar struggle to simultaneously achieve both high initial coulombic efficiency and excellent cycle performance. Summary of the Invention

[0004] The problem this invention addresses is: how to prepare hard carbon materials with both high initial coulombic efficiency and good cycling performance using wood tar as a raw material. To address the above problems, this invention provides a method for preparing hard carbon materials, comprising: Step S1: Mix wood tar and acetic acid at a preset mass ratio and stir at a preset temperature to obtain a mixture; Step S2: Under a protective gas atmosphere, the mixture is carbonized at high temperature to obtain a hard carbon material.

[0005] Optionally, in step S1, the preset mass ratio is (3 to 7):(3 to 7).

[0006] Optionally, in step S1, the preset temperature is 60°C to 150°C.

[0007] Optionally, in step S1, the stirring speed is 200 rpm to 400 rpm.

[0008] Optionally, in step S1, the stirring process takes 22 to 26 hours.

[0009] Optionally, in step S2, the protective gas atmosphere includes an argon atmosphere or a nitrogen atmosphere.

[0010] Optionally, in step S2, the high-temperature carbonization temperature is 1200°C to 1400°C.

[0011] Optionally, in step S2, the high-temperature carbonization time is 1.5h to 2.5h.

[0012] The present invention also provides a hard carbon material, which is prepared by the hard carbon material preparation method described above.

[0013] The present invention also provides the application of the hard carbon material described above in the preparation of sodium-ion batteries.

[0014] Compared with related technologies, in this invention, acetic acid can undergo esterification and polycondensation reactions with the abundant phenolic hydroxyl groups and active sites in wood tar, effectively suppressing the violent volatilization of small molecules during pyrolysis and reducing the formation of open pores. Simultaneously, the cross-linked structure formed by esterification and polycondensation makes the carbon skeleton more compact, and some pores close during carbonization shrinkage, reducing the specific surface area of ​​the material. This inhibits excessive decomposition of the electrolyte during the first charge and discharge, reduces irreversible loss of active sodium ions, and improves the initial coulombic efficiency of the material. Furthermore, the premixing of acetic acid and wood tar promotes the orderly construction of the carbon skeleton during carbonization, forming a more stable graphite-like microcrystalline structure, enhancing the structural stability of the hard carbon material, and effectively mitigating volume expansion and structural collapse during repeated sodium ion insertion and extraction, thus improving the material's cycle performance. In summary, the hard carbon material prepared by the method of this invention possesses both high initial coulombic efficiency and excellent cycle performance. Using the hard carbon material provided by this invention to prepare sodium-ion batteries can significantly improve the initial coulombic efficiency and cycle stability of sodium-ion batteries. Attached Figure Description

[0015] Figure 1 This is a low-magnification scanning electron microscope image of the hard carbon material prepared in Example 1 of the present invention; Figure 2 This is a high-magnification scanning electron microscope image of the hard carbon material prepared in Example 1 of the present invention. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0018] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the following description. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0019] This invention provides a method for preparing a hard carbon material, comprising: Step S1: Mix wood tar and acetic acid at a preset mass ratio and stir at a preset temperature to obtain a mixture; Step S2: Under a protective gas atmosphere, the mixture is carbonized at high temperature to obtain a hard carbon material.

[0020] In this embodiment of the invention, acetic acid can undergo esterification and polycondensation reactions with the abundant phenolic hydroxyl groups and active sites in wood tar, effectively inhibiting the violent volatilization of small molecules during pyrolysis and reducing the formation of open pores. Simultaneously, the cross-linked structure formed by esterification and polycondensation makes the carbon skeleton more compact, and some pores close during carbonization shrinkage, reducing the specific surface area of ​​the material. This inhibits excessive decomposition of the electrolyte during the first charge-discharge cycle, reduces irreversible loss of active sodium ions, and improves the initial coulombic efficiency of the material. Furthermore, the premixing of acetic acid and wood tar promotes the orderly construction of the carbon skeleton during carbonization, forming a more stable graphite-like microcrystalline structure, enhancing the structural stability of the hard carbon material, and effectively mitigating volume expansion and structural collapse during repeated sodium ion insertion and extraction, thus improving the material's cycling performance. In summary, the hard carbon material prepared using the method of this embodiment of the invention possesses both high initial coulombic efficiency and excellent cycling performance.

[0021] In some embodiments of the present invention, in step S1, the preset mass ratio is (3 to 7):(3 to 7). In this embodiment, by controlling the preset mass ratio to (3 to 7):(3 to 7), the synergistic effect of the carbon source and acetic acid in the precursor is ensured to reach a better level, avoiding uneven carbonization or excessive pore development caused by an excess of a certain component.

[0022] In some embodiments of the present invention, the preset temperature in step S1 is 60°C to 150°C. In this embodiment, by controlling the preset temperature to 60°C to 150°C, a balance between intermolecular crosslinking and the slow release of volatiles is achieved, reducing the surface defect density after carbonization.

[0023] In some embodiments of the present invention, in step S1, the stirring speed is 200 rpm to 400 rpm, and the stirring time is 22 h to 26 h. In this embodiment, by controlling the speed and time of the stirring process, the mixing system is ensured to be fully homogeneous, avoiding phase separation caused by excessively high local concentrations. Specifically, the stirring process can be carried out by magnetic stirring.

[0024] In some embodiments of the present invention, the protective gas atmosphere in step S2 includes an argon atmosphere or a nitrogen atmosphere. In this embodiment, the protective gas atmosphere effectively isolates oxygen, preventing the precursor from oxidizing before carbonization, while also avoiding oxidation and etching of the carbon layer structure, thus maintaining the integrity of the carbon skeleton.

[0025] In some embodiments of the present invention, in step S2, the high-temperature carbonization temperature is 1200°C to 1400°C, and the high-temperature carbonization time is 1.5h to 2.5h. In this embodiment, by controlling the temperature and time of high-temperature carbonization, it is ensured that oxygen-containing functional groups and volatiles are fully removed while avoiding excessive graphitization that would lead to interlayer shrinkage, thereby preserving the disordered carbon structure and microporous network that are conducive to sodium ion insertion / extraction.

[0026] This invention also provides a hard carbon material, which is prepared using the hard carbon material preparation method described above.

[0027] The present invention also provides the application of the hard carbon material described above in the preparation of sodium-ion batteries.

[0028] Using the hard carbon material provided in the embodiments of the present invention to prepare sodium-ion batteries can significantly improve the initial coulombic efficiency and cycle stability of sodium-ion batteries.

[0029] The present invention will be further described below with reference to specific embodiments.

[0030] Example 1 A1. Wood tar and acetic acid are mixed in a preset mass ratio and stirred at a preset temperature to obtain a mixture; wherein the preset mass ratio is 5:5, the preset temperature is 90℃, the stirring speed is 300rpm, and the time is 24h.

[0031] A2. Under an argon atmosphere, the mixture is heated to 1300°C at a preset rate and held for 2 hours to obtain a hard carbon material; wherein the preset rate is 5°C / min.

[0032] Example 2 A1. Wood tar and acetic acid are mixed at a preset mass ratio and stirred at a preset temperature to obtain a mixture; wherein the preset mass ratio is 3:7, the preset temperature is 90℃, the stirring speed is 300rpm, and the time is 24h.

[0033] A2. Under an argon atmosphere, the mixture is heated to 1300°C at a preset rate and held for 2 hours to obtain a hard carbon material; wherein the preset rate is 5°C / min.

[0034] Example 3 A1. Wood tar and acetic acid are mixed in a preset mass ratio and stirred at a preset temperature to obtain a mixture; wherein the preset mass ratio is 4:6, the preset temperature is 90℃, the stirring speed is 300rpm, and the time is 24h.

[0035] A2. Under an argon atmosphere, the mixture is heated to 1300°C at a preset rate and held for 2 hours to obtain a hard carbon material; wherein the preset rate is 5°C / min.

[0036] Example 4 The difference from Example 1 is that in step A1, the preset mass ratio is 6:4.

[0037] Example 5 The difference from Example 1 is that in step A1, the preset mass ratio is 7:3.

[0038] Example 6 The difference from Example 1 is that in step A1, the preset temperature is 60°C.

[0039] Example 7 The difference from Example 1 is that in step A1, the preset temperature is 120°C.

[0040] Example 8 The difference from Example 1 is that in step A1, the preset temperature is 150°C.

[0041] Comparative Example Wood tar was heated to 1300°C at a preset rate and held for 2 hours under an argon atmosphere to obtain hard carbon material; wherein the preset rate was 5°C / min.

[0042] Effect Example The hard carbon material prepared in Example 1 was characterized by scanning electron microscopy, and the results are shown in the figure. Figure 1 and Figure 2 ,from Figure 1 and Figure 2 It can be seen that the surface of the hard carbon material prepared in Example 1 has clear and continuous parallel layered stacked textures, which are consistent with the microstructure of hard carbon material.

[0043] The interlayer spacing of the hard carbon materials prepared in Examples 1 to 3 and the comparative example was detected by XRD. The results are shown in Table 1. As can be seen from Table 1, compared with the comparative example, the interlayer spacing of the hard carbon materials prepared in Examples 1 to 3 is larger, which is more conducive to the deintercalation and intercalation of sodium ions.

[0044] The specific surface area and total pore volume of the hard carbon materials prepared in Examples 1 to 3 and the comparative example were detected by nitrogen adsorption-desorption test. The results are shown in Table 2. As can be seen from Table 2, compared with the comparative example, the specific surface area and total pore volume of the hard carbon materials prepared in Examples 1 to 3 are smaller. This indicates that the treatment of wood tar with acetic acid can effectively control the pore structure of hard carbon, and the overall porosity of the samples is at a low level. The corresponding defect concentration in the samples is also reduced.

[0045] Table 1

[0046] Table 2

[0047] The hard carbon materials prepared in Examples 1 to 3 and the comparative examples were tested using a half-cell test method to measure their initial discharge specific capacity, initial coulombic efficiency, and capacity retention after 100 cycles. The results are shown in Table 3. As can be seen from Table 3, compared with the comparative examples, the hard carbon materials prepared in Examples 1 to 3 have higher initial discharge specific capacity, initial coulombic efficiency, and capacity retention after 100 cycles.

[0048] Table 3

[0049] It should be noted that the test conditions for the first discharge specific capacity and first coulombic efficiency in Table 3 are 0℃ and 0.3 C.

[0050] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that, include: Step S1: Mix wood tar and acetic acid at a preset mass ratio and stir at a preset temperature to obtain a mixture; Step S2: Under a protective gas atmosphere, the mixture is carbonized at high temperature to obtain a hard carbon material.

2. The method for preparing hard carbon material according to claim 1, characterized in that, In step S1, the preset mass ratio is (3 to 7): (3 to 7).

3. The method for preparing hard carbon material according to claim 1, characterized in that, In step S1, the preset temperature is 60°C to 150°C.

4. The method for preparing hard carbon material according to claim 1, characterized in that, In step S1, the stirring speed is 200 rpm to 400 rpm.

5. The method for preparing hard carbon material according to claim 1, characterized in that, In step S1, the stirring process takes 22 to 26 hours.

6. The method for preparing hard carbon material according to claim 1, characterized in that, In step S2, the protective gas atmosphere includes an argon atmosphere or a nitrogen atmosphere.

7. The method for preparing hard carbon material according to claim 1, characterized in that, In step S2, the high-temperature carbonization temperature is 1200°C to 1400°C.

8. The method for preparing hard carbon material according to claim 1, characterized in that, In step S2, the high-temperature carbonization time is 1.5h to 2.5h.

9. A hard carbon material, characterized in that, It is prepared using the method for preparing hard carbon material as described in any one of claims 1 to 8.

10. The application of the hard carbon material as described in claim 9 in the preparation of sodium-ion batteries.

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