Long-flame coal-based hard carbon negative electrode material, preparation method and secondary battery

Abstract

The application provides a long-flame coal-based hard carbon negative material, a preparation method and a secondary battery, and belongs to the technical field of battery materials. The preparation method comprises the following steps: mixing long-flame coal and water, introducing oxygen-containing gas, and sealing; then, water is converted into supercritical water by heating, a wet oxidation reaction is carried out, and an intermediate product is obtained; then, the intermediate product is subjected to carbonization treatment, and the long-flame coal-based hard carbon negative material is obtained. The supercritical water and dissolved oxygen are mutually cooperative and double-oxidized, the intensity and uniformity of the oxidation reaction between the surface of long-flame coal particles and oxygen free radicals are enhanced, the problem of uneven reaction caused by particle accumulation is avoided, efficient oxidation of long-flame coal is realized, more ion storage sites and fast ion transmission channels can be formed, and the capacity performance and initial efficiency of the long-flame coal-based hard carbon negative material are significantly improved. The method has the advantages of simplicity, low cost, no pollution, green environmental protection and the like, and has good development potential.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a long-flame coal-based hard carbon anode material, its preparation method, and a secondary battery. Background Technology

[0002] With increasing global emphasis on clean energy and sustainable development, rechargeable batteries, as a highly efficient energy storage device, have been widely used in electric vehicles, portable electronic devices, and other fields. Among these applications, the negative electrode material is one of the key factors determining the performance of rechargeable batteries.

[0003] Currently, while commonly used secondary battery anode materials such as graphite have certain performance advantages, they also have some drawbacks. For example, graphite resources are limited, its cost is high, and its performance in certain specific applications needs improvement. Therefore, finding new high-performance, low-cost anode materials has become an urgent priority.

[0004] Hard carbon is considered the most promising anode material for sodium-ion / lithium-ion batteries due to its advantages such as high capacity, low operating potential, wide availability, and low cost. Currently, research in the field of deep coal processing focuses on the development of anode materials using anthracite with a carbon content exceeding 90%. However, the narrow interlayer spacing of carbon atoms in the products obtained from the direct high-temperature carbonization of anthracite leads to slow kinetics in the electrode energy storage process, resulting in negative effects such as low capacity and low rate capability. This results in coal-based hard carbon with inherent defects such as low specific capacity and poor power performance. Furthermore, the carbon materials prepared by direct coal carbonization are mostly soft carbons with large lamellar polycyclic aromatic hydrocarbon molecular structures, which differ from hard carbon in terms of capacity and electrochemical properties. In addition, coal oxidation often employs air oxidation and acid oxidation methods, which suffer from flammability and high costs.

[0005] Therefore, how to achieve efficient oxidation of coal, so that coal can be fully converted into a hard carbon structure, and at the same time improve the capacity performance and first efficiency of coal-based hard carbon, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a long-flame coal-based hard carbon anode material, its preparation method, and a secondary battery. The preparation method provided by this invention has advantages such as simplicity, low cost, no pollution, and environmental friendliness. By utilizing the oxidation characteristics of supercritical water under high temperature and pressure, as well as the dual oxidation effect of dissolved oxygen in the water, the uniformity of the reaction between the particle surface and oxygen free radicals can be ensured, avoiding the problem of uneven reaction caused by particle accumulation. This achieves highly efficient oxidation of coal, resulting in the formation of numerous "house of cards" shaped hard carbon structures, significantly improving the capacity performance and initial efficiency of the long-flame coal-based hard carbon anode material, and demonstrating good development potential.

[0007] One objective of this invention is to provide a method for preparing a coal-based hard carbon anode material, the method comprising the following steps:

[0008] (1) After mixing long-flame coal and water, oxygen-containing gas with a pressure of 0.2-1 MPa is introduced and the reaction system is sealed;

[0009] (2) Heat the reaction system to 300-500℃ to convert water into supercritical water and carry out wet oxidation reaction to obtain intermediate products;

[0010] (3) Carbonize the intermediate product to obtain the long-flame coal-based hard carbon anode material;

[0011] The long-flame coal is in powder form.

[0012] Preferably, the pressure of the reaction system during the wet oxidation process is 20-25 MPa.

[0013] Preferably, the holding time for the wet oxidation reaction is 0.5-5 hours.

[0014] Preferably, the stirring speed of the wet oxidation reaction is 50-1000 r / min.

[0015] Preferably, the heating rate of the wet oxidation reaction in step (2) is 1-2℃ / min.

[0016] Preferably, the mass ratio of the long-flame coal to water is 1:(2-10).

[0017] Preferably, step (1) further includes adding a co-solvent during the mixing of the long-flame coal and water.

[0018] Preferably, the mass ratio of the co-solvent to water is (1-10):100.

[0019] Preferably, the long-flame coal is fine particles with a particle size D50 of 4-20 μm.

[0020] Preferably, step (2) further includes a separation and drying step after the wet oxidation reaction is completed.

[0021] Preferably, the carbonization temperature is 1200-1600℃.

[0022] Preferably, the heat preservation time for the carbonization treatment is 1-10 hours.

[0023] The second objective of this invention is to provide a long-flame coal-based hard carbon anode material, which is prepared by the preparation method described above.

[0024] A third objective of this invention is to provide a secondary battery, wherein the negative electrode of the secondary battery includes the long-flame coal-based hard carbon negative electrode material as described above.

[0025] The beneficial effects of this invention include:

[0026] This invention first mixes long-flame coal and water, then introduces oxygen-containing gas. Under high temperature and pressure, the water is converted into supercritical water for a wet oxidation reaction, followed by a carbonization reaction. The synergistic effect of supercritical water and dissolved oxygen in the water, through dual oxidation, enhances the intensity and uniformity of the oxidation reaction between the long-flame coal particles and oxygen free radicals, avoiding the problem of uneven reaction caused by particle accumulation, thus achieving highly efficient oxidation of long-flame coal. On the one hand, it introduces abundant oxygen-containing functional groups, increasing the surface activity and ion storage capacity of the hard carbon anode material. On the other hand, the organic components in the long-flame coal undergo oxidative decomposition, forming a large number of micropores and mesopores, optimizing the crystal structure and micromorphology of the long-flame coal. This makes it easier to form a layered "house of cards" structure during the carbonization process, enabling control over the hard carbon structure and providing more ion storage sites and rapid ion transport channels. The preparation method described in this invention can significantly improve the capacity performance and first-efficiency of long-flame coal-based hard carbon anode materials, and has the advantages of being simple, low-cost, pollution-free, and environmentally friendly, showing good development potential. Furthermore, the preparation method provided by this invention is simple and easy to implement in industrial scale-up processes, avoiding a large number of complex processes. Attached Figure Description

[0027] Figure 1 The process flow diagram for preparing the long-flame coal-based hard carbon anode material provided in Example 1 is shown.

[0028] Figure 2 This is a SEM image of the long-flame coal-based hard carbon anode material prepared in Example 2. Detailed Implementation

[0029] The following description includes certain specific details to provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that the embodiments can be implemented without employing one or more of these specific details, but using other methods, components, materials, etc.

[0030] Unless otherwise required by this invention, the terms “comprising” and “including” shall be interpreted in an open-ended, inclusive sense, meaning “including but not limited to”.

[0031] Throughout this specification, the terms "an embodiment," "an embodiment," "a preferred embodiment," or "some embodiments" refer to including, in at least one embodiment, a specific reference element, structure, or feature related to that embodiment. Therefore, the phrases "in an embodiment," "in a preferred embodiment," or "in some embodiments" appearing in different places throughout the specification do not necessarily all refer to the same embodiment. Furthermore, specific elements, structures, or features may be combined in one or more embodiments in any suitable manner.

[0032] According to a first aspect of the present invention, a method for preparing a coal-based hard carbon anode material is provided, the method comprising the following steps:

[0033] (1) After mixing long-flame coal and water, oxygen-containing gas with a pressure of 0.2-1 MPa is introduced and the reaction system is sealed;

[0034] (2) Heat the reaction system to 300-500℃ to convert water into supercritical water and carry out wet oxidation reaction to obtain intermediate products;

[0035] (3) Carbonize the intermediate product to obtain the long-flame coal-based hard carbon anode material;

[0036] Long-flame coal is in powder form.

[0037] Specifically, the wet oxidation reaction is carried out in a high-temperature, high-pressure reactor (such as a high-temperature, high-pressure reactor). The pressure of the oxygen-containing gas can be, for example, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, or 1 MPa, or any value between these two. The temperature of the reaction system is, for example, 350°C, 375°C, 400°C, 425°C, or 450°C, or any value between these two. The oxygen-containing gas includes air and / or oxygen.

[0038] In this invention, supercritical water refers to water at a certain pressure and temperature, where the density of water expanding due to high temperature is exactly the same as the density of water vapor compressed due to high pressure. At this point, the liquid and gaseous states of water become indistinguishable, completely mixing together to form a new fluid exhibiting a high-pressure, high-temperature state. Supercritical water has very low viscosity and a very high diffusion coefficient. Supercritical water possesses two significant characteristics: firstly, it has strong oxidizing power, acting as a strong oxidant to promote the oxidative decomposition of organic matter, and also as a catalyst to accelerate chemical reactions; secondly, it has strong solubility, exhibiting a strong ability to dissolve organic matter and also high solubility for gases.

[0039] This invention first mixes long-flame coal, then introduces oxygen-containing gas, and converts water into supercritical water under high temperature and pressure for a wet oxidation reaction, followed by a carbonization reaction. Firstly, the high temperature and pressure environment of supercritical water promotes the dissolution of oxygen-containing gas in the water, allowing dissolved oxygen to be more evenly distributed in the reaction system. Dissolved oxygen in the water can interact with supercritical water to form more oxygen free radicals. Secondly, supercritical water has a high diffusion coefficient and low viscosity, enabling oxygen free radicals to diffuse rapidly and distribute evenly in the reaction system. Thirdly, supercritical water can also dissolve some organic matter in the long-flame coal, exposing more active sites on the surface of coal particles, which is beneficial for the full contact and reaction between oxygen free radicals and the coal particle surface. The synergistic effect of supercritical water and oxygen-containing gas enhances the intensity and uniformity of the oxidation reaction. The synergistic and dual oxidation of supercritical water and dissolved oxygen in the water enhances the intensity and uniformity of the oxidation reaction between the surface of long-flame coal particles and oxygen free radicals, avoiding the problem of uneven reaction caused by particle accumulation, thus achieving efficient oxidation of long-flame coal.

[0040] Efficient oxidation of long-flame coal can introduce abundant oxygen-containing functional groups, increasing the surface activity and ion storage capacity of hard carbon anode materials. It also oxidizes and decomposes the organic components in long-flame coal, forming numerous micropores and mesopores, optimizing the crystal structure and micromorphology of the coal. This makes it easier to form a layered "house of cards" structure during carbonization, enabling control over the hard carbon structure and providing more ion storage sites and rapid ion transport channels. Ultimately, this improves the capacity performance and first-efficiency of long-flame coal-based hard carbon anode materials, and offers advantages such as simplicity, low cost, no pollution, and environmental friendliness, demonstrating significant development potential.

[0041] In a preferred embodiment of the present invention, the pressure of the reaction system in the wet oxidation process is 20-25 MPa, for example, it can be 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa or 25 MPa, and any value between the two mentioned above.

[0042] In this invention, a pressure of 20-25 MPa and a reaction temperature of 350-450°C facilitate the complete conversion of water into supercritical water. The supercritical state of water under high temperature and pressure ensures the uniformity of the reaction between the particle surface and oxygen free radicals, avoiding the problem of uneven reaction caused by particle accumulation. Simultaneously, the oxidation properties of supercritical water and the dual oxidation effect of dissolved oxygen in the water enable highly efficient oxidation of coal. If the pressure or reaction temperature is too low, water cannot be fully converted into supercritical water, resulting in a weakened oxidation reaction intensity and reduced efficiency. This makes it difficult to induce the necessary structural adjustments in long-flame coal, thus affecting the capacity performance and initial efficiency of the hard carbon anode material. If the pressure or reaction temperature is too high, excessively high temperatures or pressures may degrade the stability of the reaction system, posing a risk of over-oxidation of coal, damaging its original structure, and also posing challenges to reaction equipment and safety.

[0043] Preferably, the holding time for the wet oxidation reaction is 0.5-5h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, and any value between the two mentioned above.

[0044] Preferably, the stirring speed of the wet oxidation reaction is 50-1000 r / min, for example, it can be 50 r / min, 100 r / min, 150 r / min, 200 r / min, 400 r / min, 600 r / min, 800 r / min or 1000 r / min, and any value between the two mentioned above, preferably 100-200 r / min.

[0045] In a preferred embodiment of the present invention, the heating rate of the wet oxidation reaction in step (2) is 1-2℃ / min, for example, it can be 1℃ / min, 1.2℃ / min, 1.4℃ / min, 1.5℃ / min, 1.6℃ / min, 1.8℃ / min or 2℃ / min, and any value between the two mentioned above.

[0046] In this invention, a slow heating rate and long heating time affect the preparation efficiency of coal-based hard carbon. At the same time, a slow heating rate causes the carbon to remain in a certain temperature range for a long time, which affects the formation of effective functional group structures on the coal surface and results in poor electrochemical properties of the final hard carbon. If the heating rate is too fast, it may lead to uneven temperature distribution inside the reaction system, which may result in over-oxidation in some areas and insufficient oxidation in others. It may also damage the structure of long-flame coal, thereby reducing the quality and performance of the hard carbon anode material.

[0047] In a preferred embodiment of the present invention, the mass ratio of the long-flame coal to water is 1:(2-10), for example, it can be 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, as well as any point value between the two mentioned above.

[0048] In this invention, if the mass ratio of long-flame coal to water is too small, the amount of water used will be too large, which may change the properties of supercritical water, causing it to deviate from the optimal reaction state. It may also dilute the oxygen-containing substances dissolved in the water, reducing the intensity of the oxidation reaction.

[0049] If the mass ratio of long-flame coal to water is too large, i.e., water is relatively less, it may cause the long-flame coal particles to be in closer contact, making it easy for particles to accumulate. This makes it difficult to ensure that the surface of the long-flame coal particles reacts fully with supercritical water and dissolved oxygen. It may also make it difficult to fully transform into the supercritical water state under given temperature and pressure conditions, affecting the reaction rate and uniformity.

[0050] Specifically, the water may be deionized water.

[0051] In a preferred embodiment of the present invention, step (1) further includes adding a co-solvent during the mixing of the long-flame coal and water.

[0052] In this invention, the co-solvent improves the hydrophilicity of the long-flame coal surface, facilitating its dispersion in water and preventing particle aggregation. This, in turn, helps ensure sufficient contact between the long-flame coal particles and supercritical water and oxygen-containing gases during subsequent reactions, improving reaction uniformity and efficiency. The co-solvent also interacts with the long-flame coal, introducing additional active sites on its surface. Furthermore, it increases the solubility of oxygen-containing gases in water and promotes their diffusion within the reaction system, making the oxidation reaction more controllable.

[0053] Preferably, the co-solvent includes any one or a combination of at least two of ethanol, acetic acid, hydrogen peroxide or Tween, and more preferably a combination of ethanol, Tween, hydrogen peroxide and acetic acid.

[0054] It should be noted that Tween is a nonionic surfactant with strong hydrophilicity, a pH of about 6-8, and is stable to electrolytes, weak acids, and weak bases.

[0055] Preferably, the mass ratio of the co-solvent to the water is (1-10):100, for example, it can be 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100, as well as any point value between the two mentioned above.

[0056] In a preferred embodiment of the present invention, the long-flame coal is a fine particle with a particle size D50 of 4-20 μm, for example, it can be 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm, and any point value between the two mentioned above.

[0057] In this invention, if the particle size is too small, the long-flame coal particles may easily agglomerate and be difficult to disperse evenly, affecting the uniformity of the overall reaction; if the particle size is too large, the specific surface area of ​​the long-flame coal particles is relatively small, which will reduce the rate and efficiency of the oxidation reaction, and may lead to insufficient oxidation reaction. Larger particles may have difficulty forming a uniform "house of cards" hard carbon structure in the subsequent carbonization process.

[0058] In a preferred embodiment of the present invention, step (2) further includes a separation and drying step after the wet oxidation reaction is completed.

[0059] In this invention, the separation is performed using a centrifugal separation method, and the centrifuged liquid obtained by centrifugation can be recycled.

[0060] Preferably, after the wet oxidation reaction is completed, the product is centrifuged at 500-1500 rpm (e.g., 500 rpm, 750 rpm, 1000 rpm, 1250 rpm or 1500 rpm) for 20-60 min (e.g., 20 min, 30 min, 40 min, 50 min or 60 min) and then dried at 100-120℃ (e.g., 100℃, 105℃, 110℃, 115℃ or 120℃) for 8-12 h to obtain the intermediate product.

[0061] In a preferred embodiment of the present invention, the carbonization temperature is 1200-1600℃, for example, it can be 1200℃, 1300℃, 1400℃, 1500℃ or 1600℃, and any value between the two mentioned above.

[0062] Preferably, the heat preservation time for the carbonization treatment is 1-10h, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, and any value between the two mentioned above.

[0063] Preferably, the carbonization process is carried out in an inert atmosphere, such as nitrogen or argon.

[0064] Preferably, the heating rate of the carbonization treatment is 1-10℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, and any value between the two mentioned above.

[0065] In a preferred embodiment of the present invention, the preparation method includes the following steps:

[0066] (1) The long-flame coal is crushed to obtain fine particles with a particle size D50 of 4-20 μm. Then, it is mixed with water and a co-solvent and added to a high-temperature and high-pressure reaction device. Then, oxygen-containing gas with a pressure of 0.2-1 MPa is introduced and the device is sealed.

[0067] The mass ratio of long-flame coal to water is 1:(2-10), and the mass ratio of flux to water is (1-10):100.

[0068] (2) The sealed high-temperature and high-pressure reaction device described in step (1) is heated to 350-450℃ at a heating rate of 1-2℃ / min, while the pressure of the high-temperature and high-pressure reaction device is 20-25MPa, so that the water is converted into supercritical water and a wet oxidation reaction is carried out for 0.5-5h. After the reaction is completed, the device is centrifuged at a speed of 500-1500rpm for 20-60min, and then dried at 100-120℃ for 8-12h to obtain the intermediate product.

[0069] (3) Under an inert atmosphere, the intermediate product is heated to 1200-1600℃ at a heating rate of 1-10℃ / min and carbonized for 1-10h to obtain the long-flame coal-based hard carbon anode material.

[0070] According to a second aspect of the present invention, a long-flame coal-based hard carbon anode material is provided, which is prepared by the preparation method described in the first aspect.

[0071] According to a third aspect of the present invention, a secondary battery is provided, wherein the negative electrode of the secondary battery comprises the long-flame coal-based hard carbon negative electrode material as described above.

[0072] Preferably, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0073] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0074] Example

[0075] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0076] In the following embodiments, unless otherwise specified, all raw material components are commercially available products.

[0077] Example 1

[0078] This embodiment provides a method for preparing a long-flame coal-based hard carbon anode material, and its preparation process flow diagram is shown below. Figure 1 As shown, the preparation method includes the following steps:

[0079] (1) The long-flame coal is crushed to obtain fine particles with a particle size D50 of 12 μm. Then, it is mixed with deionized water and a co-solvent and added to a high-temperature and high-pressure reaction device. Then, oxygen at a pressure of 0.6 MPa is introduced and the device is sealed.

[0080] The mass ratio of long-flame coal to deionized water is 1:8, the fluxing agent is Tween, and the mass ratio of fluxing agent to deionized water is 5:100.

[0081] (2) The sealed high-temperature and high-pressure reaction device described in step (1) is heated to 374°C at a heating rate of 1.5°C / min, and the pressure of the high-temperature and high-pressure reaction device is 22MPa, so that the water is converted into supercritical water. The wet oxidation reaction is carried out for 3 hours at a stirring speed of 150r / min. After the reaction is completed, the reaction product is centrifuged at a speed of 1000rpm for 40min, and then dried at 110°C for 10h to obtain the intermediate product.

[0082] The centrifuged liquid obtained from centrifugation can be recycled back into the wet oxidation reaction.

[0083] (3) Under a nitrogen atmosphere, the intermediate product is heated to 1400°C at a heating rate of 5°C / min and carbonized for 5 hours to obtain the long-flame coal-based hard carbon anode material.

[0084] Example 2

[0085] This embodiment provides a method for preparing a long-flame coal-based hard carbon anode material, the method comprising the following steps:

[0086] (1) The long-flame coal is crushed to obtain fine particles with a particle size D50 of 4 μm. Then, it is mixed with deionized water and a co-solvent and added to a high-temperature and high-pressure reaction device. Then, oxygen at a pressure of 0.2 MPa is introduced and the device is sealed.

[0087] The mass ratio of long-flame coal to deionized water is 1:5, the co-solvent is acetic acid, and the mass ratio of co-solvent to deionized water is 1:100.

[0088] (2) The sealed high-temperature and high-pressure reaction device described in step (1) is heated to 374°C at a heating rate of 1°C / min, and the pressure of the high-temperature and high-pressure reaction device is 22MPa, so that the water is converted into supercritical water. The wet oxidation reaction is carried out for 1 hour at a stirring speed of 150r / min. After the reaction is completed, the mixture is centrifuged at a speed of 500rpm for 60min, and then dried at 100°C for 12 hours to obtain the intermediate product.

[0089] (3) Under an argon atmosphere, the intermediate product is heated to 1200°C at a heating rate of 1°C / min and carbonized for 10 hours to obtain the long-flame coal-based hard carbon anode material.

[0090] Example 3

[0091] This embodiment provides a method for preparing a long-flame coal-based hard carbon anode material, the method comprising the following steps:

[0092] (1) The long-flame coal is crushed to obtain fine particles with a particle size D50 of 15 μm. Then, it is mixed with deionized water and a co-solvent and added to a high-temperature and high-pressure reaction device. Then, air with a pressure of 1 MPa is introduced and the device is sealed.

[0093] The mass ratio of long-flame coal to deionized water is 1:10, the co-solvent is hydrogen peroxide, and the mass ratio of co-solvent to deionized water is 10:100.

[0094] (2) The sealed high-temperature and high-pressure reaction device described in step (1) is heated to 374°C at a heating rate of 2°C / min, and the pressure of the high-temperature and high-pressure reaction device is 22MPa, so that the water is converted into supercritical water. The wet oxidation reaction is carried out for 1 hour at a stirring speed of 150r / min. After the reaction is completed, the mixture is centrifuged at a speed of 1500rpm for 20min, and then dried at 120°C for 8 hours to obtain the intermediate product.

[0095] (3) Under a nitrogen atmosphere, the intermediate product is heated to 1600°C at a heating rate of 10°C / min and carbonized for 1 hour to obtain the long-flame coal-based hard carbon anode material.

[0096] Example 4

[0097] The difference between this embodiment and embodiment 1 is that the temperature of the high-temperature and high-pressure reaction device in step (2) is 350°C after heating, and the pressure of the high-temperature and high-pressure reaction device is 15MPa, which makes the water transform into near-supercritical water.

[0098] The remaining preparation methods and parameters are consistent with those in Example 1.

[0099] Example 5

[0100] The difference between this embodiment and embodiment 1 is that the temperature of the high-temperature and high-pressure reaction device in step (2) is 450°C after heating, and the pressure of the high-temperature and high-pressure reaction device is 40MPa, which makes the water transform into supercritical water.

[0101] The remaining preparation methods and parameters are consistent with those in Example 1.

[0102] Example 6

[0103] The difference between this embodiment and Embodiment 1 is that no co-solvent is added in step (1).

[0104] The remaining preparation methods and parameters are consistent with those in Example 1.

[0105] Example 7

[0106] The difference between this embodiment and embodiment 1 is that the temperature of the high-temperature and high-pressure reaction device in step (2) after heating is 300℃.

[0107] The remaining preparation methods and parameters are consistent with those in Example 1.

[0108] Example 8

[0109] The difference between this embodiment and embodiment 1 is that the temperature of the high-temperature and high-pressure reaction device in step (2) after heating is 500℃.

[0110] The remaining preparation methods and parameters are consistent with those in Example 1.

[0111] Example 9

[0112] The difference between this embodiment and embodiment 1 is that the mass ratio of long-flame coal and water in step (1) is 1:10.

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] Example 10

[0115] The difference between this embodiment and embodiment 1 is that the mass ratio of long-flame coal and water in step (1) is 1:5.

[0116] The remaining preparation methods and parameters are consistent with those in Example 1.

[0117] Example 11

[0118] The difference between this embodiment and embodiment 1 is that the mass ratio of the cosolvent and water in step (1) is 1:100.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Example 12

[0121] The difference between this embodiment and embodiment 1 is that the mass ratio of the cosolvent and water in step (1) is 10:100.

[0122] The remaining preparation methods and parameters are consistent with those in Example 1.

[0123] Comparative Example 1

[0124] The difference between this comparative example and Example 1 is that in step (1), the high-temperature and high-pressure reaction device is not sealed, so that after the high-temperature and high-pressure reaction device is heated, the water is completely converted into water vapor.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Comparative Example 2

[0127] The difference between this comparative example and Example 1 is that the oxygen introduced in step (1) is replaced with nitrogen.

[0128] The remaining preparation methods and parameters are consistent with those in Example 1.

[0129] Comparative Example 3

[0130] This comparative example provides a method for preparing a long-flame coal-based hard carbon anode material, the method comprising the following steps:

[0131] Long-flame coal is crushed to obtain fine particles with a particle size D50 of 15 μm.

[0132] Long-flame coal was subjected to acid oxidation treatment with nitric acid at a mass ratio of 1:10 for 1 hour at a temperature of 80°C, and the concentration of nitric acid was 5 mol / L.

[0133] After the reaction was completed, the product was centrifuged at 1500 rpm for 20 min and then dried at 120 °C for 8 h to obtain the intermediate product.

[0134] The dried intermediate product was heated to 1600°C at a heating rate of 10°C / min under a nitrogen atmosphere and carbonized for 1 hour to obtain the long-flame coal-based hard carbon anode material.

[0135] Performance testing

[0136] (1) The microstructure of the long-flame coal-based hard carbon anode material prepared in Example 2 was characterized, and its SEM image is shown below. Figure 2 As shown.

[0137] (2) First, the long-flame coal-based hard carbon negative electrode material is made into a negative electrode sheet. The preparation method of the negative electrode sheet includes: mixing the prepared hard carbon, conductive carbon black (Super P), carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) into a slurry according to a formula ratio of 91:2:2:5. The prepared slurry is coated onto a carbon-coated copper foil, and then transferred to a 65°C forced-air drying oven until the electrode sheet is dry (about 1-2 h), and then transferred to a vacuum drying oven for 12 h to obtain the negative electrode sheet.

[0138] Then, the negative electrode sheet is assembled with the positive electrode sheet sodium sheet, polyethylene separator and carbonate electrolyte to obtain a sodium-ion battery.

[0139] The electrochemical performance of the above-mentioned sodium-ion batteries was tested, including capacity performance and initial efficiency. The charge-discharge test conditions were: voltage range 0-2V, current density 30mA·g −1 The reversible capacity and first efficiency were obtained by conducting charge and discharge tests.

[0140] The test results are shown in Table 1.

[0141] Table 1. Test results of Examples 1-12 and Comparative Examples 1-3

[0142]

[0143] analyze:

[0144] As shown in the table above, the preparation method provided by this invention has the advantages of being simple, easy to implement, low-cost, pollution-free, and environmentally friendly. By utilizing the oxidation characteristics of supercritical water under high temperature and pressure and the dual oxidation effect of dissolved oxygen in water, the uniformity of the reaction between the particle surface and oxygen free radicals can be ensured, avoiding the problem of uneven reaction caused by particle accumulation. This achieves efficient oxidation of coal, resulting in the formation of a large number of "house of cards" shaped hard carbon structures in the coal, which significantly improves the capacity performance and first-efficiency of long-flame coal-based hard carbon anode materials, and has good development potential.

[0145] As can be seen from Examples 1, 4-5, and 7-8, if the temperature or pressure after the high-temperature and high-pressure reactor is too low, the oxidation effect on long-flame coal particles will be poor, which may result in insufficient formation of the hard carbon "house of cards" configuration, and low reversible capacity and first-time efficiency of the hard carbon. If the temperature or pressure after the high-temperature and high-pressure reactor is too high, the oxidation effect on long-flame coal particles will be too sufficient, resulting in a large number of pore structures. These pores are difficult to close after subsequent carbonization treatment, resulting in low reversible capacity and first-time efficiency of the hard carbon.

[0146] As can be seen from Examples 1 and 6, if no co-solvent is added in step (1), the long-flame coal and water cannot be completely wetted and mixed evenly, resulting in poor uniformity of the long-flame coal reaction in the subsequent wet oxidation process.

[0147] As can be seen from Examples 1 and 9-10, if the mass ratio of long-flame coal to water is too small, the reaction is prone to deviating from the optimal reaction state, and may also dilute the oxygen-containing substances dissolved in the water, reducing the intensity of the oxidation reaction, resulting in lower reversible capacity and first-time efficiency of hard carbon. If the mass ratio of long-flame coal to water is too large, particle accumulation is likely to occur, and it may also lead to difficulty in fully converting to the supercritical water state under given temperature and pressure conditions, affecting the reaction rate and uniformity, resulting in lower reversible capacity and first-time efficiency of hard carbon.

[0148] As can be seen from Examples 1 and 11-12, if the amount of co-solvent is too small, the reaction uniformity of long-flame coal is likely to be poor; if the amount of co-solvent is too large, it may trigger side reactions and may interfere with the structural formation of long-flame coal in the subsequent carbonization process; if the amount of co-solvent is too small or too large, it is easy to form an unsuitable hard carbon structure, which will lead to a decrease in the capacity performance and cycle stability of the material.

[0149] As can be seen from Example 1 and Comparative Example 1, if the high-temperature and high-pressure reaction device is not sealed in step (1), the water will be completely converted into water vapor after the high-temperature and high-pressure reaction device is heated, and a large amount of water vapor will escape and will not be able to oxidize the long-flame coal.

[0150] As can be seen from Example 1 and Comparative Example 2, if the oxygen introduced in step (1) is replaced with nitrogen, the long-flame coal exhibits surface inertness during the wet oxidation process under high temperature and high pressure, resulting in a poor oxidation effect on the interior of the long-flame coal particles.

[0151] As can be seen from Example 1 and Comparative Example 3, if conventional technology is used to prepare long-flame coal-based hard carbon anode materials, the prepared hard carbon has poor electrochemical and capacity properties, and the acid waste liquid generated during the preparation process is difficult to treat, causing environmental pollution.

[0152] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a long-flame coal-based hard carbon anode material, characterized in that, The preparation method includes the following steps: (1) After mixing long-flame coal and water, oxygen-containing gas with a pressure of 0.2-1 MPa is introduced and the reaction system is sealed; (2) Heat the reaction system to 300-500℃ to convert water into supercritical water and carry out wet oxidation reaction to obtain intermediate products; (3) Carbonize the intermediate product to obtain the long-flame coal-based hard carbon anode material; The long-flame coal is in powder form; In the wet oxidation process, the pressure of the reaction system is 20-25 MPa, the holding time of the wet oxidation reaction is 0.5-5 h, and the stirring speed is 50-1000 r / min; The mass ratio of the long-flame coal to water is 1:(2-10). Step (1) also includes adding a co-solvent during the mixing of the long-flame coal and water, wherein the mass ratio of the co-solvent to water is (1-10):100; The co-solvent includes any one or a combination of at least two of acetic acid, hydrogen peroxide, or Tween. The carbonization temperature is 1200-1600℃, and the holding time for the carbonization is 1-10h.

2. The preparation method according to claim 1, characterized in that, The heating rate of the wet oxidation reaction in step (2) is 1-2℃ / min.

3. The preparation method according to claim 1, characterized in that, The long-flame coal is fine particles with a particle size D50 of 4-20 μm.

4. The preparation method according to claim 1, characterized in that, Step (2) also includes the steps of separation and drying after the wet oxidation reaction is completed.

5. A long-flame coal-based hard carbon anode material, characterized in that, The long-flame coal-based hard carbon anode material is prepared using the preparation method described in any one of claims 1-4.

6. A secondary battery, characterized in that, The negative electrode of the secondary battery includes the long-flame coal-based hard carbon negative electrode material as described in claim 5.

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