A pitch-based amorphous carbon material and a method for producing the same

Abstract

This invention relates to the field of sodium-ion battery anode material technology, and proposes a pitch coke-based amorphous carbon material and its preparation method. The pitch coke-based amorphous carbon material includes porous pitch coke-based hard carbon and amorphous carbon coated on the surface of the porous pitch coke-based hard carbon. The raw materials for the porous pitch coke-based hard carbon include pitch coke powder and a pore-forming agent. The pore-forming agent comprises NaOH and KCl. This technical solution solves the problems of low capacity and low initial coulombic efficiency of pitch coke-based anode materials in related technologies.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, specifically to a pitch coke-based amorphous carbon material and its preparation method. Background Technology

[0002] With the increasing depletion of fossil fuels, the demand for renewable energy and related large-scale energy storage systems continues to rise, leading to rapid development in battery technology and applications. Lithium-ion batteries have seen rapid development in recent years; however, the low abundance and uneven geographical distribution of lithium resources mean that limited resources cannot meet the market demand for lithium-ion batteries, posing a significant challenge to their long-term large-scale production. Sodium, belonging to the same group as lithium, is abundant and widely distributed, and these two alkali metals share a similar "rocking chair" working principle in their respective ion batteries. Therefore, sodium-ion batteries hold promise as a widely used energy storage device following lithium-ion batteries.

[0003] The thermodynamic instability of the compound formed between sodium ions and graphite means that graphite, a commercially available anode material for lithium-ion batteries, cannot be directly used in sodium-ion batteries. Therefore, finding a suitable anode material for sodium storage is crucial. Amorphous carbon includes soft carbon and hard carbon. Hard carbon, with its larger interlayer spacing and disordered structure, is more conducive to the insertion and extraction of sodium ions, making it an ideal anode material for sodium-ion batteries.

[0004] There are many precursors for preparing hard carbon, such as biomass, phenolic resins, and polymers. Resin-based precursors are often expensive and not suitable for large-scale production. While biomass precursors are widely available, some raw materials, such as coconut shells, are subject to import and export restrictions, leading to difficulties in obtaining raw materials and significantly increasing transportation and labor costs. This limits their application in sodium-ion battery anode materials in the Chinese market. Furthermore, these precursors are generally expensive. Pitch coke, on the other hand, is cheaper and more widely available. However, untreated pitch coke easily forms graphite-like structures during carbonization, resulting in low specific capacity and initial coulombic efficiency when hard carbon prepared from pitch coke is used as an anode material. Therefore, pitch coke needs to be treated to improve its specific capacity and initial coulombic efficiency when used as an anode material. Summary of the Invention

[0005] This invention proposes a pitch coke-based amorphous carbon material and its preparation method, which solves the problems of low capacity and low initial coulombic efficiency of pitch coke-based anode materials in related technologies.

[0006] The technical solution of the present invention is as follows:

[0007] This invention proposes a pitch coke-based amorphous carbon material, comprising porous pitch coke-based hard carbon and amorphous carbon coated on the surface of the porous pitch coke-based hard carbon.

[0008] The raw materials for the porous pitch coke-based hard carbon include pitch coke powder and a pore-forming agent.

[0009] The pore-forming agent comprises NaOH and KCl.

[0010] As a further technical solution, the mass ratio of NaOH to KCl is 1:1~4.

[0011] As a further technical solution, the mass ratio of the asphalt coke powder to the pore-forming agent is 1:1~2.

[0012] As a further technical solution, the particle size of the pitch coke powder is 5~6μm.

[0013] This invention also proposes a method for preparing pitch coke-based amorphous carbon material, comprising the following steps:

[0014] S1. After mixing the pitch coke powder and the pore-forming agent, the mixture is first carbonized under a nitrogen atmosphere, then cooled under an oxygen atmosphere, and finally acid-washed to neutral to obtain porous pitch coke-based hard carbon.

[0015] S2. The porous pitch coke-based hard carbon and organic acid are mixed and then carbonized to obtain pitch coke-based amorphous carbon material.

[0016] In this invention, in step S1, the nitrogen atmosphere is changed to an oxygen atmosphere, thereby introducing oxygen elements, increasing the number of carbon-oxygen covalent bonds, thus hindering the degree of crosslinking of graphitization, and further improving the capacity and first coulombic efficiency of the pitch coke-based amorphous carbon material as a negative electrode material.

[0017] As a further technical solution, the organic acid is one or more of tartaric acid, malic acid, and 4,5-trihydroxybenzoic acid, preferably 4,5-trihydroxybenzoic acid.

[0018] In this invention, the coating layer is formed by the pyrolysis of organic acids, which increases the number of closed pores inside the material. In particular, when 4,5-trihydroxybenzoic acid is used, the capacity and first coulombic efficiency of the pitch coke-based amorphous carbon material as a negative electrode material are further improved.

[0019] As a further technical solution, in step S1, the carbonization process involves heating the temperature to 900-1000℃ at a rate of 2-5℃ / min and then holding it at that temperature for 1-3 hours.

[0020] As a further technical solution, in step S2, the carbonization process involves heating the temperature to 1300-1500℃ at a rate of 2-5℃ / min and then holding it at that temperature for 1-3 hours.

[0021] As a further technical solution, the mass ratio of the porous pitch coke-based hard carbon to organic acid is 1:0.1~0.3.

[0022] As a further technical solution, the interlayer spacing of the pitch coke-based amorphous carbon material is 0.345~0.371nm, and the particle size D50 is 7~11μm.

[0023] In this invention, a compounded pore-forming agent, a mixed salt template, and high-temperature carbonization were used to obtain a pitch coke hard carbon anode material with a large interlayer spacing and suitable porosity, thereby improving the initial coulombic efficiency. Secondly, pitch coke, as a product of pitch calcination, has lower cost and wider availability. This preparation method transforms pitch coke, a soft carbon material, into a hard carbon material suitable for sodium storage, further reducing costs and promoting the commercialization of sodium-ion battery anode materials.

[0024] The working principle and beneficial effects of this invention are as follows:

[0025] In this invention, pitch coke, as a soft carbon material that can be graphitized, is activated and pore-forming by preparing a pore-forming agent using a mixture of NaOH and KCl. The resulting product can penetrate into the microcrystalline structure of the pitch coke, and as the temperature rises, it etches into the carbon layer, eventually volatilizing as vapor. Micropores are formed at the etched sites, which become channels for sodium ion insertion. The pore structure can be adjusted by controlling the dosage, significantly improving the capacity and first coulombic efficiency of the pitch coke-based amorphous carbon material as a negative electrode material. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] A method for preparing pitch coke-based amorphous carbon materials includes the following steps:

[0029] S1. Pitch coke powder with a particle size of 5~6μm is mechanically mixed with a pore-forming agent at a mass ratio of 1:1. After stirring evenly, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 900℃ at a heating rate of 3℃ / min. The temperature is then maintained for 3 hours, followed by cooling to room temperature with oxygen and acid washing until neutral to obtain porous pitch coke-based hard carbon. The pore-forming agent is NaOH and KCl in a mass ratio of 1:3.

[0030] S2. After mixing porous pitch coke-based hard carbon with 4,5-trihydroxybenzoic acid at a mass ratio of 1:0.2, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 1400℃ at a heating rate of 3℃ / min, and then held at that temperature for 3 hours to obtain pitch coke-based amorphous carbon material.

[0031] Example 2

[0032] The only difference between this embodiment and Embodiment 1 is that in step S1, the asphalt coke powder and the pore-forming agent are mechanically mixed at a mass ratio of 1:2.

[0033] Example 3

[0034] The only difference between this embodiment and Embodiment 1 is that in step S1, the temperature is increased to 900°C at a heating rate of 3°C / min and then held for 1 hour.

[0035] Example 4

[0036] The only difference between this embodiment and Embodiment 1 is that the pore-forming agent is NaOH and KCl in a mass ratio of 1:2.

[0037] Example 5

[0038] The only difference between this embodiment and Embodiment 1 is that the pore-forming agent is NaOH and KCl in a mass ratio of 1:4.

[0039] Example 6

[0040] The only difference between this embodiment and Embodiment 3 is that 4,5-trihydroxybenzoic acid is replaced with tartaric acid.

[0041] Example 7

[0042] The only difference between this embodiment and Embodiment 3 is that 4,5-trihydroxybenzoic acid is replaced with malic acid.

[0043] Example 8

[0044] A method for preparing pitch coke-based amorphous carbon materials includes the following steps:

[0045] S1. Pitch coke powder with a particle size of 5~6μm is mechanically mixed with a pore-forming agent at a mass ratio of 1:1. After stirring evenly, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 900℃ at a heating rate of 3℃ / min. The temperature is then maintained for 3 hours, cooled to room temperature, and acid-washed until neutral to obtain porous pitch coke-based hard carbon. The pore-forming agent is NaOH and KCl in a mass ratio of 1:3.

[0046] S2. After mixing porous pitch coke-based hard carbon with 4,5-trihydroxybenzoic acid at a mass ratio of 1:0.2, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 1400℃ at a heating rate of 3℃ / min, and then held at that temperature for 3 hours to obtain pitch coke-based amorphous carbon material.

[0047] Example 9

[0048] A method for preparing pitch coke-based amorphous carbon materials includes the following steps:

[0049] S1. Pitch coke powder with a particle size of 5~6μm is placed in a carbonization furnace at 300℃ under an oxygen atmosphere and allowed to stand. It is then mechanically mixed with a pore-forming agent at a mass ratio of 1:1. After stirring evenly, it is placed in a carbonization furnace under a nitrogen atmosphere and heated to 900℃ at a heating rate of 3℃ / min. The temperature is then maintained for 3 hours. Subsequently, the mixture is replaced with oxygen and cooled to room temperature. It is then acid-washed until neutral to obtain porous pitch coke-based hard carbon. The pore-forming agent is NaOH and KCl in a mass ratio of 1:3.

[0050] S2. After mixing porous pitch coke-based hard carbon with 4,5-trihydroxybenzoic acid at a mass ratio of 1:0.2, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 1400℃ at a heating rate of 3℃ / min, and then held at that temperature for 3 hours to obtain pitch coke-based amorphous carbon material.

[0051] Example 10

[0052] A method for preparing pitch coke-based amorphous carbon materials includes the following steps:

[0053] S1. Pitch coke powder with a particle size of 5~6μm and a pore-forming agent are mechanically mixed at a mass ratio of 1:1. After stirring evenly, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 1000℃ at a heating rate of 5℃ / min. The temperature is then maintained for 1 hour, followed by cooling to room temperature with oxygen and acid washing until neutral to obtain porous pitch coke-based hard carbon. The pore-forming agent is NaOH and KCl in a mass ratio of 1:3.

[0054] S2. After mixing porous pitch coke-based hard carbon with 4,5-trihydroxybenzoic acid at a mass ratio of 1:0.1, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 1500℃ at a heating rate of 5℃ / min, and then held at that temperature for 1 hour to obtain pitch coke-based amorphous carbon material.

[0055] Example 11

[0056] A method for preparing pitch coke-based amorphous carbon materials includes the following steps:

[0057] S1. Pitch coke powder with a particle size of 5~6μm is mechanically mixed with a pore-forming agent at a mass ratio of 1:1. After stirring evenly, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 950℃ at a heating rate of 2℃ / min. The temperature is then maintained for 2 hours, followed by cooling to room temperature with oxygen and acid washing until neutral to obtain porous pitch coke-based hard carbon. The pore-forming agent is NaOH and KCl in a mass ratio of 1:3.

[0058] S2. After mixing porous pitch coke-based hard carbon with 4,5-trihydroxybenzoic acid at a mass ratio of 1:0.3, the mixture is placed in a carbonization furnace under a nitrogen atmosphere and heated to 1300℃ at a heating rate of 2℃ / min, and then held at that temperature for 2 hours to obtain pitch coke-based amorphous carbon material.

[0059] Comparative Example 1

[0060] The only difference between this embodiment and Embodiment 1 is that the pore-forming agent is NaOH.

[0061] Comparative Example 2

[0062] The only difference between this embodiment and Embodiment 1 is that the pore-forming agent is KCl.

[0063] Comparative Example 3

[0064] The only difference between this comparative example and Example 1 is that no pore-forming agent is added in step S1.

[0065] Comparative Example 4

[0066] A method for preparing pitch coke-based amorphous carbon materials includes the following steps:

[0067] Pitch coke powder with a particle size of 5~6μm was mechanically mixed with a pore-forming agent at a mass ratio of 1:1. After stirring evenly, the mixture was placed in a carbonization furnace under a nitrogen atmosphere and heated to 900℃ at a heating rate of 3℃ / min. The temperature was then maintained for 3 hours, followed by cooling to room temperature with oxygen and acid washing until neutral to obtain pitch coke-based amorphous carbon material. The pore-forming agent was NaOH and KCl in a mass ratio of 1:3.

[0068] Using pitch coke-based hard carbon anode material as the anode, sodium sheet as the cathode, 1 mol NaPF6 / DEGDME as the electrolyte, and double-sided PCS coating as the separator (substrate PZ×12 μm, 3 μm CCS double-sided 1.5 mg PCS), electrochemical tests were conducted at a rate of 0.1C. In addition, XRD and particle size tests were performed on the prepared hard carbon material. The specific test results are shown in Table 1.

[0069] Table 1 Test Results

[0070]

[0071] Compared with Comparative Examples 1-3, Example 1, which uses a pore-forming agent prepared by mixing NaOH and KCl to activate and create pores in pitch coke, shows that the capacity and first coulombic efficiency of the material are higher. This indicates that using a pore-forming agent prepared by mixing NaOH and KCl significantly improves the capacity and first coulombic efficiency of pitch coke-based amorphous carbon material as a negative electrode material.

[0072] Compared with Examples 8-9, the pitch coke-based amorphous carbon material prepared in Example 1 has higher capacity and initial coulombic efficiency, indicating that the carbonization in step S1 under a nitrogen atmosphere followed by a cooling treatment under an oxygen atmosphere further improves the capacity and initial coulombic efficiency of the pitch coke-based amorphous carbon material as a negative electrode material.

[0073] Compared with Comparative Example 4, the pitch coke-based amorphous carbon material prepared in Example 1 has higher capacity and first coulombic efficiency, indicating that the formation of a coating layer through the cracking of organic acids increases the number of closed pores inside the material, thereby improving the capacity and first coulombic efficiency of the pitch coke-based anode material as an anode material.

[0074] Compared with Examples 6-7, the pitch coke-based amorphous carbon material prepared in Example 3 has higher capacity and initial coulombic efficiency, indicating that the use of 4,5-trihydroxybenzoic acid cracking of organic acid further improves the capacity and initial coulombic efficiency of pitch coke-based amorphous carbon material as a negative electrode material.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a pitch-based amorphous carbon material, characterized by, Includes the following steps: S1. After mixing the pitch coke powder and the pore-forming agent, the mixture is first carbonized under a nitrogen atmosphere, then cooled under an oxygen atmosphere, and finally acid-washed to neutral to obtain porous pitch coke-based hard carbon. S2. The porous pitch coke-based hard carbon and organic acid are mixed and then carbonized to obtain pitch coke-based amorphous carbon material; the pitch coke-based amorphous carbon material includes porous pitch coke-based hard carbon and amorphous carbon coated on the surface of the porous pitch coke-based hard carbon. The pore-forming agent comprises NaOH and KCl; the organic acid is 4,5-trihydroxybenzoic acid.

2. The process for the preparation of pitch-based carbon materials according to claim 1, characterized in that, The mass ratio of NaOH to KCl is 1:1~4.

3. The method for preparing a pitch coke-based amorphous carbon material according to claim 1, characterized in that, The mass ratio of the asphalt coke powder to the pore-forming agent is 1:1~2.

4. The method for preparing a pitch coke-based amorphous carbon material according to claim 1, characterized in that, The particle size of the asphalt coke powder is 5~6μm.

5. The method for preparing a pitch coke-based amorphous carbon material according to claim 1, characterized in that, In step S1, during carbonization, the temperature is increased to 900-1000℃ at a heating rate of 2-5℃ / min and then held for 1-3 hours.

6. The method for preparing a pitch coke-based amorphous carbon material according to claim 1, characterized in that, In step S2, during carbonization, the temperature is increased to 1300-1500℃ at a heating rate of 2-5℃ / min and then held for 1-3 hours.

7. The method for preparing a pitch coke-based amorphous carbon material according to claim 1, characterized in that, The mass ratio of the porous pitch coke-based hard carbon to organic acid is 1:0.1~0.

3.

8. The method for preparing a pitch coke-based amorphous carbon material according to claim 1, characterized in that, The interlayer spacing of the pitch coke-based amorphous carbon material is 0.345~0.371nm, and the particle size D50 is 7~11μm.

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