Asphalt-based hard carbon material as well as pre-oxidation preparation method and application thereof

Abstract

The invention discloses an asphalt-based hard carbon material as well as a pre-oxidation preparation method and application thereof. Belongs to the technical field of asphalt-based hard carbon materials. The pre-oxidation preparation method comprises the following steps: carrying out primary pre-oxidation treatment on asphalt at 250-400 DEG C in air flow of 50-500mL / min; crushing the obtained primary pre-oxidized asphalt, and then carrying out secondary pre-oxidation treatment at 250-400 DEG C in air flow of 50-500mL / min to obtain secondary pre-oxidized asphalt; and carrying out carbonization treatment on the secondary pre-oxidized asphalt. According to the method, the asphalt can be kept in a solid-phase state to be subjected to efficient and thorough oxidation cross-linking reaction, the production cost is reduced, the obtained asphalt-based hard carbon material has high first coulombic efficiency and high capacity, and powerful support is provided for commercial application of sodium-ion battery negative electrode materials and rapid development of an energy storage technology.

Description

Technical Field

[0001] This invention relates to the technical field of pitch-based hard carbon materials, and particularly to pitch-based hard carbon materials, their pre-oxidation preparation methods, and applications. Background Technology

[0002] Sodium-ion batteries are considered a next-generation energy storage device with the potential for large-scale development due to their abundant resources, low cost, long lifespan, and good safety performance. However, the current lack of low-cost electrode materials, especially negative electrode materials, significantly limits the development of sodium-ion batteries. Therefore, developing low-cost, high-performance electrode materials is an urgent technical problem to be solved.

[0003] Asphalt, as a low-cost carbon precursor, can be transformed into hard carbon materials through oxidative crosslinking, showing great potential for large-scale production and industrial applications. The preparation of hard carbon materials requires the introduction of oxygen functional groups via oxidative crosslinking to control the carbon layer arrangement during carbonization and adjust the material's micro / nano structure and surface properties. Currently, low-cost, green preparation methods often employ air pre-oxidation of asphalt, typically carried out in a pusher furnace or rotary kiln. However, relying solely on a single pre-oxidation treatment leads to severe melting and agglomeration of the asphalt when production volumes reach tens of grams or even kilograms, and this cannot be significantly improved by extending the oxidation time, temperature, pressure, or airflow rate. In the pusher process, the asphalt layer thickness is often less than 1 cm, and the rotary kiln's processing capacity is also relatively small. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a novel asphalt-based hard carbon material and its pre-oxidation preparation method and application. The pre-oxidation preparation method includes a secondary pre-oxidation treatment process, which keeps the asphalt in a solid state and maintains the high efficiency of the oxidative crosslinking reaction. This can greatly improve the melting and hardening of asphalt during carbonization, enhance the oxidation uniformity and oxygen crosslinking degree of asphalt, and enable the asphalt-based hard carbon material to achieve high initial coulombic efficiency and high capacity.

[0005] The technical solution of the present invention is as follows: A method for pre-oxidizing and preparing an asphalt-based hard carbon material, comprising: Asphalt is pre-oxidized once by subjecting it to an air stream to obtain pre-oxidized asphalt. The pre-oxidized asphalt is crushed to a particle size of 3~15μm to obtain pre-oxidized asphalt granules; The pre-oxidized asphalt aggregate is subjected to a secondary pre-oxidation treatment in an air stream to obtain secondary pre-oxidized asphalt. When observing whether there is liquid phase melting or caking after liquid phase melting in the obtained secondary pre-oxidized asphalt, if there is, repeat the secondary pre-oxidation treatment several times until there is no liquid phase melting in the obtained secondary pre-oxidized asphalt, and then carry out carbonization treatment. If there is no liquid phase melting, carry out carbonization treatment directly. The secondary pre-oxidized asphalt is subjected to carbonization treatment to obtain asphalt-based hard carbon material. The airflow velocity is 50~500mL / min; the temperature of the first pre-oxidation treatment is 250~400℃, and the holding time is 1~10h; the temperature of the second pre-oxidation treatment is 250~400℃, and the holding time is 1~10h.

[0006] The liquid phase melting mentioned in the above technical solution refers to the phenomenon of molten liquid or semi-liquid (i.e., liquid mixed with solid) appearing in asphalt. The phenomenon of caking after liquid phase melting is manifested as follows: because molten liquid or semi-liquid has appeared in asphalt, asphalt particles adhere to each other, and after cooling, they present as hard, lumpy, and difficult-to-flow solid blocks with a significant glossy black surface.

[0007] The inventors unexpectedly discovered that the limitations of rotary kiln pre-oxidation treatment or pusher furnace pre-oxidation treatment in the prior art on the asphalt paving thickness or asphalt feeding amount are due to the following reasons: incomplete asphalt oxidation reaction and low degree of cross-linking. During the heat treatment process, the incompletely oxidized and low-cross-linked asphalt undergoes a liquid phase reaction, resulting in foaming and melting, which leads to a high soft carbon phase in the obtained product and reduces sodium storage performance. On the other hand, excessive oxygen introduction increases the surface defects of the obtained hard carbon material, increases the adsorption energy of sodium ions, and makes it difficult for sodium ions to detach from the hard carbon surface, reducing the initial efficiency of the battery.

[0008] Therefore, the above technical solution of the present invention improves the air pre-oxidation process, achieves a balance between the initial efficiency and capacity of the obtained pitch-based hard carbon material, not only ensures the basic performance of the material, but also fully stimulates its electrochemical performance, while significantly reducing production costs and obtaining high-performance hard carbon material.

[0009] In the above technical solutions, the secondary pre-oxidation process can further functionalize the unoxidized surfaces and melted agglomerates in the product obtained from the primary pre-oxidation treatment by breaking them up and exposing new surfaces. This promotes deep cross-linking of asphalt, keeps the asphalt interface in a solid-phase reaction state during the secondary oxidation process, ensures good dispersion between particles, avoids melting and caking in asphalt-based hard carbon during production, helps improve product consistency and reduce production costs, and obtains high-performance hard carbon materials.

[0010] According to some preferred embodiments of the present invention, the asphalt is petroleum asphalt and / or coal tar pitch with a softening point above 200°C and a particle size of 5 to 50 μm.

[0011] According to some preferred embodiments of the present invention, the airflow is formed from dry air with a moisture content of less than 2.0 ppm, and contains nitrogen and oxygen at a volume percentage of 20.5 ± 0.5%.

[0012] According to some preferred embodiments of the present invention, the heating rate in the primary pre-oxidation treatment is 0.5~5℃ / min.

[0013] According to some preferred embodiments of the present invention, the heating rate in the secondary pre-oxidation treatment is 0.5~10℃ / min.

[0014] According to some preferred embodiments of the present invention, the carbonization treatment includes: heating the secondary pre-oxidized asphalt to 400~600℃, i.e., the first temperature range, and holding it at that temperature for 1~6 hours, then heating it to 1200~1600℃, i.e., the second temperature range, and holding it at that temperature for 1~6 hours, followed by natural cooling.

[0015] According to some preferred embodiments of the present invention, the heating rate to the first temperature range is 1~10℃ / min.

[0016] According to some preferred embodiments of the present invention, the heating rate to the second temperature range is 1~5℃ / min.

[0017] According to some preferred embodiments of the present invention, the pre-oxidation preparation method further includes: when liquid phase melting occurs in the obtained secondary pre-oxidized asphalt, repeating the secondary pre-oxidation treatment several times until no liquid phase melting occurs in the obtained product, and then performing the carbonization treatment.

[0018] According to some preferred embodiments of the present invention, the primary pre-oxidation treatment and / or the secondary pre-oxidation treatment are carried out in a pusher furnace or / or a rotary kiln.

[0019] According to some preferred embodiments of the present invention, the softening point of the asphalt is 280°C, and the particle size D is... 50 =5μm; the airflow velocity is 200mL / min; the temperature of the first pre-oxidation treatment is 350℃ and the holding time is 2h; the temperature of the second pre-oxidation treatment is 350℃ and the holding time is 2h.

[0020] The inventors unexpectedly discovered that this preferred embodiment can simultaneously achieve better first discharge specific capacity, first charge specific capacity, and first coulombic efficiency.

[0021] The present invention further provides a pitch-based hard carbon material obtained according to the above preparation method.

[0022] The resulting asphalt-based hard carbon material has a specific surface area of ​​<5m².2 / g, ash content <1%, interplanar spacing >0.37nm, tap density >0.8g / cm³ 3 .

[0023] This invention further provides the application of the above-mentioned pitch-based hard carbon material in the negative electrode of sodium-ion batteries.

[0024] In some specific embodiments, the sodium-ion battery obtained by applying the asphalt-based hard carbon material to the negative electrode of a sodium-ion battery has an initial coulombic efficiency of >90% and a discharge specific capacity of >300mAh / g.

[0025] This invention can significantly improve the efficiency and uniformity of asphalt oxidation crosslinking, and can flexibly adjust the degree of crosslinking to optimize the hard carbon structure. It breaks through the limitations of the thickness of the push plate and the rotary feeding when only one pre-oxidation is used, and improves the pre-oxidation yield. At the same time, the electrochemical performance of the prepared hard carbon is significantly improved, and the product quality is higher.

[0026] The preparation method of the present invention enables asphalt to undergo efficient oxidative crosslinking reaction in a solid state, which can greatly improve the melting and caking of asphalt during carbonization, ensure good dispersion between particles, improve the oxidation uniformity and oxygen crosslinking degree of asphalt, and enable asphalt-based hard carbon materials to achieve both high initial coulombic efficiency and high capacity. The preparation method of the present invention can greatly stimulate the electrochemical potential of pitch-based hard carbon materials, improve their capacity as electrode materials, and have good product consistency in mass production. The preparation method of the present invention can increase the asphalt paving thickness and / or feeding amount in the traditional preparation, reduce production costs, and improve the industrial application potential of asphalt-based hard carbon materials. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process for preparing pitch-based hard carbon materials in an embodiment of the present invention.

[0028] Figure 2 This is a comparison image of the pre-oxidized products of Example 2 and Comparative Example 2 of the present invention. Detailed Implementation

[0029] The technical solutions of the present invention will be further described below with reference to the embodiments and accompanying drawings. The embodiments described below 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 should fall within the scope of protection of the present invention.

[0030] The preparation method of the following embodiments is shown in the attached figure. Figure 1 As shown.

[0031] Example 1: A method for preparing pitch-based hard carbon materials using the following steps: (1) Take 50g of material with a softening point of 250℃ and particle size D. 50 =5μm petroleum asphalt is placed in a rotary kiln and subjected to a pre-oxidation treatment in air to obtain pre-oxidized asphalt; wherein, the pre-oxidation treatment process is as follows: at an air flow rate of 200mL / min, the temperature is raised to 350℃ at a heating rate of 2℃ / min, held at the temperature for 2h, and then cooled to room temperature with the furnace. (2) The pre-oxidized asphalt was crushed by ball milling at a speed of 300 rpm for 2 hours. After crushing, it was sieved through a 600-mesh sieve to obtain pre-oxidized asphalt granules. (3) The pre-oxidized asphalt aggregate was placed in a rotary kiln for secondary pre-oxidation treatment to obtain secondary pre-oxidized asphalt; the secondary pre-oxidation treatment process was as follows: under dry air atmosphere, the temperature was raised to 350℃ at a heating rate of 2℃ / min, held for 2h, and then cooled to room temperature with the furnace; it was observed that the primary pre-oxidized asphalt exhibited liquid phase melting, while the secondary pre-oxidized asphalt did not exhibit liquid phase melting. (4) The secondary pre-oxidized asphalt was carbonized under nitrogen with a purity of 99.999%. The process was as follows: the temperature was raised to 450°C at a heating rate of 2°C / min and held for 2 hours. Then the temperature was raised from 450°C to 1400°C at a heating rate of 2°C / min and held for 3 hours. After that, the asphalt-based hard carbon material was obtained by cooling it to room temperature in a protective atmosphere.

[0032] Example 2: A method for preparing pitch-based hard carbon materials using the following steps: (1) Take 7g of material with a softening point of 250℃ and particle size D. 50 =5μm petroleum asphalt was placed in a flat crucible and subjected to a pre-oxidation treatment in a tube furnace to obtain pre-oxidized asphalt. The pre-oxidation treatment process was as follows: the temperature was increased to 350℃ at a heating rate of 1℃ / min under an air flow rate of 200mL / min, held for 2h, and then cooled to room temperature with the furnace. (2) The pre-oxidized asphalt was crushed by ball milling at a speed of 300 rpm for 2 hours. After crushing, it was sieved through a 600-mesh sieve to obtain pre-oxidized asphalt granules. (3) The pre-oxidized asphalt aggregate was placed in a flat crucible for secondary pre-oxidation treatment to obtain secondary pre-oxidized asphalt. The secondary pre-oxidation treatment process was as follows: under dry air atmosphere, the temperature was raised to 350℃ at a heating rate of 1℃ / min, held for 2h, and then cooled to room temperature with the furnace. It was observed that the primary pre-oxidized asphalt exhibited liquid phase melting, while the secondary pre-oxidized asphalt did not exhibit liquid phase melting. (4) The secondary pre-oxidized asphalt was carbonized under nitrogen with a purity of 99.999%. The process was as follows: the temperature was raised to 450°C at a heating rate of 2°C / min and held for 2 hours. Then the temperature was raised from 450°C to 1400°C at a heating rate of 2°C / min and held for 3 hours. After that, the asphalt-based hard carbon material was obtained by cooling it to room temperature in a protective atmosphere.

[0033] Example 3: Asphalt-based hard carbon material was prepared using the same steps as in Example 2, the only difference being that the softening point of the petroleum asphalt was 280°C. Observation showed that the primary pre-oxidized asphalt exhibited liquid-phase melting, while the secondary pre-oxidized asphalt did not.

[0034] Example 4: Asphalt-based hard carbon materials were prepared using the same steps as in Example 1, except that the softening point of the petroleum asphalt was 180°C and the insulation temperature for the two pre-oxidations was changed to 300°C. It was observed that the asphalt exhibited liquid-phase melting in both the first and second pre-oxidations.

[0035] Comparative Example 1: Asphalt-based hard carbon materials were prepared using the same steps as in Example 1, except that a secondary pre-oxidation treatment, i.e., step (3), was not performed. It was observed that the pre-oxidized asphalt exhibited liquid-phase melting.

[0036] Comparative Example 2: Asphalt-based hard carbon materials were prepared using the same steps as in Example 2, except that a secondary pre-oxidation treatment, i.e., step (3), was not performed. It was observed that the pre-oxidized asphalt exhibited liquid-phase melting.

[0037] Comparative Example 3: Asphalt-based hard carbon materials were prepared using the same steps as in Example 3, except that a secondary pre-oxidation treatment, i.e., step (3), was not performed. It was observed that the pre-oxidized asphalt exhibited liquid-phase melting.

[0038] Comparative Example 4: Asphalt-based hard carbon materials were prepared using the same steps as in Example 4, except that a secondary pre-oxidation treatment, i.e., step (3), was not performed. It was observed that the pre-oxidized asphalt exhibited liquid-phase melting.

[0039] Comparative Example 5: Asphalt-based hard carbon material was prepared using the same steps as in Example 2, except that step (3) was repeated after the second pre-oxidation treatment, i.e., the same third pre-oxidation treatment was performed before step (4). It was observed that the first pre-oxidized asphalt exhibited liquid phase melting, while the second pre-oxidized asphalt and the third pre-oxidized asphalt did not exhibit liquid phase melting.

[0040] Comparative Example 6: Asphalt-based hard carbon materials were prepared using the same steps as in Example 3, except that step (3) was repeated after the second pre-oxidation treatment, i.e., the same third pre-oxidation treatment was performed before step (4). It was observed that the first pre-oxidized asphalt exhibited liquid phase melting, while the second pre-oxidized asphalt and the third pre-oxidized asphalt did not exhibit liquid phase melting.

[0041] Comparative Example 7: Asphalt-based hard carbon material was prepared using the same steps as in Example 4, except that step (3) was repeated after the second pre-oxidation treatment, i.e., the same third pre-oxidation treatment was performed before step (4). It was observed that the first pre-oxidized asphalt exhibited liquid phase melting, the second pre-oxidized asphalt exhibited liquid phase melting, and the third pre-oxidized asphalt did not exhibit liquid phase melting.

[0042] The physical comparison diagrams of the secondary pre-oxidized asphalt in Example 2 and the primary pre-oxidized asphalt in Comparative Example 2 are attached. Figure 2 As shown, where, Figure 2 (a) is the pre-oxidized asphalt of Example 2, which has a soft texture, spreads evenly, and shows no liquid phase melting or molten agglomeration. Figure 2 (b) is the pre-oxidized asphalt of Comparative Example 2, which is harder and exhibits obvious liquid phase melting and caking phenomena.

[0043] Furthermore, after homogenizing the asphalt-based hard carbon material samples obtained in Examples 1-4 and Comparative Examples 1-7, they were coated onto copper foil using a 100 μm thick tetrahedron, resulting in a surface load of 3.0~5.0 mg / cm². 2 The negative electrode plate, A 2032 coin cell sodium-ion battery was assembled in an Ar protective glove box using a sodium metal sheet as the counter electrode, a glass fiber (Waterman GF / D) membrane as the separator, and a 1M NaPF6 EC and DMC (volume ratio 1:1) solution as the electrolyte.

[0044] The obtained sodium-ion battery was subjected to constant current and constant voltage charge-discharge tests at 0.1C within a voltage range of 0.001~2.5V, with a cutoff rate of 0.01C. The test results are shown in Table 1. Table 1. Statistical Table of Test Results

[0045] It can be seen that the capacity of the sample obtained by only one pre-oxidation treatment is limited. After two pre-oxidation treatments, the capacity of the sample is significantly improved, and the initial coulombic efficiency is also improved. However, after three pre-oxidation treatments, due to the introduction of excess oxygen, the number of defect sites increases, the initial discharge capacity increases, and the initial coulombic efficiency decreases.

[0046] It can be seen that samples treated with secondary pre-oxidation can significantly stimulate the electrochemical potential of pitch-based hard carbon materials and improve the capacity of electrode materials.

[0047] Furthermore, a 50g-scale trial of the secondary pre-oxidation process of the present invention shows that the process also has the potential to optimize product performance in mass production, exhibiting a reversible capacity of >300mAh / g and an initial coulombic efficiency of >90%, demonstrating practical application potential.

[0048] It should be noted that the above descriptions are merely preferred embodiments of the present invention and should not limit the scope of protection of the technical solutions of the present invention. Any modifications made to the technical solutions described in the foregoing embodiments, or equivalent substitutions of technical features, by those skilled in the art within the spirit and principles of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for the pre-oxidation preparation of pitch-based hard carbon material, characterized in that, It comprises: carrying out a first pre-oxidation treatment on the pitch in an air flow to obtain a first pre-oxidized pitch; crushing the first pre-oxidized pitch to a particle size of 3-15 μm to obtain pre-oxidized pitch granules; carrying out a second pre-oxidation treatment on the pre-oxidized pitch granules in an air flow to obtain a second pre-oxidized pitch; observing whether there is a phenomenon of liquid phase melting or solidification after liquid phase melting in the obtained second pre-oxidized pitch, if there is, repeating the second pre-oxidation treatment for several times, until there is no phenomenon of liquid phase melting in the obtained second pre-oxidized pitch, and then carrying out carbonization treatment, if there is not, directly carrying out carbonization treatment; carrying out carbonization treatment on the second pre-oxidized pitch to obtain a pitch-based hard carbon material; The flow rate of the air flow is 50-500 mL / min; the temperature of the first pre-oxidation treatment is 250-400 ℃, and the holding time is 1-10 h; the temperature of the second pre-oxidation treatment is 250-400 ℃, and the holding time is 1-10 h.

2. The pre-oxidation production method according to claim 1, characterized in that, The pitch is petroleum pitch and / or coal pitch with a softening point of 200 ℃ or higher and a particle size of 5-50 μm.

3. The pre-oxidation production method according to claim 1, characterized in that, The air flow is formed by dry air with a moisture content of less than 2.0 ppm, containing nitrogen and oxygen with a volume percentage of 20.5±0.5%.

4. The pre-oxidation production method according to claim 1, wherein The heating rate in the first pre-oxidation treatment is 0.5-5 ℃ / min; and / or, the heating rate in the second pre-oxidation treatment is 0.5-10 ℃ / min.

5. The pre-oxidation production method according to claim 1, wherein The carbonization treatment comprises: heating the second pre-oxidized pitch to a first temperature interval of 400-600 ℃, holding for 1-6 h, then heating to a second temperature interval of 1200-1600 ℃, holding for 1-6 h, and then naturally cooling.

6. The pre-oxidation production method according to claim 5, wherein The heating rate for heating to the first temperature interval is 1-10 ℃ / min; and / or, the heating rate for heating to the second temperature interval is 1-5 ℃ / min.

7. The pre-oxidation production method according to claim 1, wherein The first pre-oxidation treatment and / or the second pre-oxidation treatment is carried out in a push plate furnace or / and a rotary furnace.

8. The pre-oxidation production method according to claim 1, wherein, The softening point of the pitch is 280°C, the particle size D 50 = 5 μm; the flow rate of the air stream is 200 mL / min; the temperature of the first pre-oxidation treatment is 350°C, and the holding time is 2 h; the temperature of the second pre-oxidation treatment is 350°C, and the holding time is 2 h.

9. A pitch-based hard carbon material prepared by the preparation method according to any one of claims 1-8.

10. Use of the pitch-based hard carbon material according to claim 9 in a sodium ion battery negative electrode.

Images