Coal-based carbon material, and preparation method and application thereof

Abstract

This invention belongs to the field of sodium-ion battery technology, specifically relating to a coal-based carbon material, its preparation method, and its application. The invention provides a method for preparing a coal-based carbon material, comprising the following steps: mixing coal and inorganic salts, ball milling in an oxygen-containing atmosphere, removing the inorganic salts from the mixture to obtain a coal-based precursor; and carbonizing the coal-based precursor to obtain the coal-based carbon material. By adding inorganic salts during ball milling, this invention effectively prevents coal agglomeration, further improves the contact efficiency between coal and oxygen, and disrupts the macromolecular structure of coal. Furthermore, after removing the inorganic salts, subsequent carbonization yields a coal-based carbon material with high carbonization yield, large interlayer spacing, and high amorphousness. Applying the coal-based carbon material provided by this invention to the anode material of sodium-ion batteries results in batteries with high sodium storage capacity and initial coulombic efficiency.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a coal-based carbon material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, as a novel type of rechargeable battery, possess advantages such as low cost, abundant resources, high cost-effectiveness, and good safety, making them widely applicable in low- and medium-speed electric vehicles and large-scale energy storage. Currently, to further improve the performance of sodium-ion batteries, it is necessary to enhance the sodium storage capacity of the electrode materials. However, due to the large radius of sodium ions, it is difficult for them to undergo intercalation / deintercalation reactions in traditional graphite anode materials, thus necessitating the development of novel sodium-ion battery anode materials.

[0003] Currently, amorphous carbon materials are considered ideal anode materials for sodium-ion batteries due to their stable structure and excellent sodium storage performance. Coal, as a high-carbon organic matter, is diverse and abundant, and can be classified into anthracite, bituminous coal, lignite, etc., according to different degrees of coalification. Hu Yongsheng et al. (Li Y, Hu Y S, Qi X, et al. Advanced sodium-ion batteries using superior low-cost pyrolyzed anthracite anode: towards practical applications[J]. Energy Storage Materials, 2016.) disclosed a method for preparing amorphous carbon materials by direct pyrolysis of anthracite. However, the amorphous carbon materials obtained have a low sodium storage capacity (220 mAh·g) due to their small interlayer spacing and high degree of order in the graphite microcrystals. -1 ).

[0004] Chinese patent CN114335522A discloses a method of oxidizing coal-based materials with sulfur-containing reagents and other oxidizing agents, followed by high-temperature carbonization to obtain coal-based carbon anode materials. However, pre-oxidation with strong oxidizing agents introduces excessive oxygen, leading to a significant reduction in coal carbonization yield, and the resulting anode material has a sodium storage capacity of only 280 mAh·g. -1 However, it still suffers from the drawback of low capacity. Summary of the Invention

[0005] The purpose of this invention is to provide a coal-based carbon material, its preparation method, and its application. The method provided by this invention has a high carbonization yield, and the obtained coal-based carbon material has a higher sodium storage capacity and a better first coulombic efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing coal-based carbon materials, comprising the following steps:

[0008] Coal and inorganic salts are mixed and ball-milled in an oxygen-containing atmosphere to remove the inorganic salts from the mixture, thus obtaining a coal-based precursor.

[0009] The coal-based precursor is carbonized to obtain the coal-based carbon material.

[0010] Preferably, the coal includes one or more of anthracite, bituminous coal, sub-bituminous coal, and lignite.

[0011] Preferably, the inorganic salt includes water-soluble inorganic salts.

[0012] Preferably, the mass ratio of coal to inorganic salt is 1-10:1-10.

[0013] Preferably, the volume fraction of oxygen in the oxygen-containing atmosphere is 10-30%.

[0014] Preferably, the ball mill rotates at a speed of 400–1000 rpm for 12–48 hours.

[0015] Preferably, the carbonization is carried out in a protective atmosphere.

[0016] Preferably, the carbonization temperature is 800–1400°C, the heating rate to the carbonization time is 0.5–10°C / min, and the holding time is 0.5–5h.

[0017] The present invention also provides a coal-based carbon material prepared by the preparation method described above, wherein the interlayer spacing of the coal-based carbon material is 0.370 to 0.376 nm.

[0018] This invention also provides the application of the coal-based carbon material described in the above technical solution as a negative electrode material for sodium-ion batteries.

[0019] This invention provides a method for preparing a coal-based carbon material, comprising the following steps: mixing coal and inorganic salts, ball milling in an oxygen-containing atmosphere, removing the inorganic salts from the mixture to obtain a coal-based precursor; and carbonizing the coal-based precursor to obtain the coal-based carbon material. This invention, by adding inorganic salts during ball milling, effectively prevents coal agglomeration, further improves the contact efficiency between coal and oxygen, effectively disrupts the macromolecular aromatic skeleton structure of coal, reduces its crosslinking density, and decreases aliphatic side chain structures and heterocyclic structures. Furthermore, since ball milling in an oxygen-containing atmosphere introduces some oxygen-containing functional groups, these fill defects during carbonization, reducing the specific surface area of ​​the carbon material. Subsequent carbonization after removing the inorganic salts yields a coal-based carbon material with high carbonization yield, large interlayer spacing, and high amorphousness. Applying the coal-based carbon material provided by this invention to sodium-ion battery anode materials results in batteries with higher sodium storage capacity and better initial coulombic efficiency. Attached Figure Description

[0020] Figure 1 SEM image of the coal-based carbon material obtained in Example 1;

[0021] Figure 2 The image shows the XRD pattern of the coal-based carbon material obtained in Example 1.

[0022] Figure 3 The XRD pattern of the coal-based carbon material obtained in Comparative Example 1;

[0023] Figure 4 The image shows the HRTEM image of the coal-based carbon material obtained in Example 1.

[0024] Figure 5 Here are the HRTEM images of the coal-based carbon materials obtained in Comparative Example 1;

[0025] Figure 6 The charge-discharge curves of a sodium-ion battery prepared using the coal-based carbon material obtained in Example 1 as the electrode material are shown.

[0026] Figure 7 The charge-discharge curves of a sodium-ion battery prepared using the coal-based carbon material obtained in Example 2 as the electrode material are shown.

[0027] Figure 8 The charge-discharge curves of a sodium-ion battery prepared using the coal-based carbon material obtained in Example 3 as the electrode material are shown.

[0028] Figure 9 The charge-discharge curves of a sodium-ion battery prepared using the coal-based carbon material obtained in Example 4 as the electrode material are shown.

[0029] Figure 10The charge-discharge curves of the sodium-ion battery prepared using the coal-based carbon material obtained in Comparative Example 1 as the electrode material are shown.

[0030] Figure 11 The charge-discharge curves of the sodium-ion battery prepared using the coal-based carbon material obtained in Comparative Example 2 as the electrode material are shown.

[0031] Figure 12 The diagram shows the cycle performance of a sodium-ion battery prepared using the coal-based carbon material obtained in Example 1 as the electrode material. Detailed Implementation

[0032] This invention provides a method for preparing coal-based carbon materials, comprising the following steps:

[0033] Coal and inorganic salts are mixed and ball-milled in an oxygen-containing atmosphere to remove the inorganic salts from the mixture, thus obtaining a coal-based precursor.

[0034] The coal-based precursor is carbonized to obtain the coal-based carbon material.

[0035] In this invention, unless otherwise specified, all raw materials are commercially available products well known to those skilled in the art.

[0036] This invention involves mixing coal and inorganic salts, ball milling the mixture in an oxygen-containing atmosphere to remove the inorganic salts and obtain a coal-based precursor.

[0037] In this invention, the coal preferably includes one or more of anthracite, bituminous coal, sub-bituminous coal and lignite; when the coal is preferably two or more of the above selections, this invention does not have a special limitation on the proportion of the specific substances, and they can be mixed in any proportion.

[0038] In this invention, the inorganic salt preferably includes a water-soluble inorganic salt. Specifically, the water-soluble inorganic salt preferably includes one or more of sodium chloride, potassium chloride, sodium sulfate, sodium carbonate, and sodium nitrate. When the water-soluble inorganic salt is preferably two or more of the above-mentioned selections, this invention does not impose a specific limitation on the proportion of the specific substances, and they can be mixed in any proportion.

[0039] In this invention, the mass ratio of coal to inorganic salt is preferably 1-10:1-10, more preferably 2-9:2-9, and even more preferably 3-8:3-8.

[0040] Before the mixing, the present invention preferably includes pretreatment of the coal; the pretreatment process preferably includes sequentially crushing, acid washing, and alkali washing of the coal. The present invention does not have a specific limitation on the crushing process; any process well known to those skilled in the art can be used. In the present invention, the crushing is preferably carried out in a crusher.

[0041] In a specific embodiment of the present invention, the reagent used for acid washing is preferably a hydrochloric acid solution; the molar concentration of the hydrochloric acid solution is preferably 3 mol / L; the reagent used for alkaline washing is preferably a sodium hydroxide solution; the molar concentration of the sodium hydroxide solution is preferably 3 mol / L. The present invention does not impose any special limitations on the acid washing and alkaline washing processes, and processes well known to those skilled in the art can be used. In the present invention, ash in coal can be removed through acid washing and alkaline washing.

[0042] The present invention does not impose any special limitations on the mixing process; any process known to those skilled in the art can be used.

[0043] In this invention, the ball milling is carried out in an oxygen-containing atmosphere. Preferably, the volume fraction of oxygen in the oxygen-containing atmosphere is 10-30%, more preferably 12-28%, and even more preferably 15-25%.

[0044] In this invention, the ball milling speed is preferably 400–1000 rpm, more preferably 500–900 rpm, and even more preferably 600–800 rpm; the ball-to-material ratio is preferably 5–30:1, more preferably 10–20:1; and the time is preferably 12–48 h, more preferably 15–45 h, and even more preferably 24–40 h. In this invention, the ball milling is preferably carried out in a ball mill.

[0045] In this invention, when the inorganic salt is a water-soluble inorganic salt, the preferred method for removing the inorganic salt from the mixture is water washing. This invention does not impose any particular limitation on the water washing process; any process well-known to those skilled in the art can be used. In this invention, the washing liquid obtained from the water washing is preferably evaporated and crystallized to obtain a water-soluble inorganic salt, which is then reused as a raw material for ball milling.

[0046] Following the water washing, the present invention preferably further includes drying the obtained product. The present invention does not specifically limit the drying process; any process well-known to those skilled in the art can be used.

[0047] After obtaining the coal-based precursor, the present invention carbonizes the coal-based precursor to obtain the coal-based carbon material.

[0048] In this invention, the carbonization is preferably carried out in a protective atmosphere; the protective atmosphere preferably includes one or more of nitrogen, helium, argon, neon and xenon.

[0049] In this invention, the carbonization temperature is preferably 800–1400°C, more preferably 900–1300°C, and even more preferably 1000–1200°C; the heating rate to the carbonization time is preferably 0.5–10°C / min, more preferably 1.0–9.0°C / min, and even more preferably 2.0–8.0°C / min; the holding time is preferably 0.5–5 h, more preferably 1.0–4.5 h, and even more preferably 1.5–4.0 h. In this invention, the carbonization is preferably carried out in a tube furnace.

[0050] After carbonization, the present invention preferably further includes sequentially cooling, removing impurities, washing with water, and drying the obtained carbonized product. In the present invention, the cooling method is preferably natural cooling to room temperature. In the present invention, the removal of impurities preferably includes sequential acid boiling and water boiling. In the present invention, the acidic reagent used for acid boiling preferably includes hydrochloric acid solution and / or sulfuric acid solution; the molar concentration of the acidic reagent is preferably 3 mol / L; the acid boiling time is preferably 2-4 hours. The present invention does not have a special limitation on the acid boiling process, and a process well known to those skilled in the art can be used. In the present invention, the water used for water boiling is preferably deionized water; the water boiling time is preferably 2-4 hours. The present invention does not have a special limitation on the water boiling process, and a process well known to those skilled in the art can be used. In the present invention, the water used for water washing is preferably deionized water. The present invention does not have a special limitation on the water washing process, as long as the pH value of the product is washed to neutral. The present invention does not have a special limitation on the drying process, and a process well known to those skilled in the art can be used.

[0051] The present invention also provides a coal-based carbon material prepared by the preparation method described in the above technical solution. In the present invention, the interlayer spacing of the coal-based carbon material is preferably 0.370–0.376 nm.

[0052] In this invention, the amorphousness (I) of the coal-based carbon material D / I G The preferred value is 1.37. In this invention, the carbonization yield of the coal-based carbon material is preferably 68% or higher.

[0053] This invention also provides the application of the coal-based carbon material described in the above technical solution as a negative electrode material for sodium-ion batteries. This invention does not impose any special limitations on the specific implementation of the application; any method well-known to those skilled in the art can be used.

[0054] To further illustrate the present invention, a coal-based carbon material, its preparation, and its application are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0055] Example 1

[0056] Anthracite was crushed using a crusher, and then acid-washed with a 3 mol / L hydrochloric acid solution and alkaline-washed with a 3 mol / L sodium hydroxide solution to obtain pretreated anthracite.

[0057] 10g of pretreated anthracite and 10g of sodium chloride were mixed and placed in a ball mill and ball-milled in an oxygen-containing atmosphere (the ball mill speed was 500 rpm, the ball-to-material ratio was 20:1, the time was 24h, and the volume fraction of oxygen in the oxygen-containing atmosphere was 21%). After ball milling, the resulting mixture was washed with water to remove sodium chloride and dried to obtain anthracite precursor.

[0058] The obtained anthracite precursor was placed in a tube furnace and carbonized in a nitrogen atmosphere at a heating rate of 5℃ / min to 1200℃, and held at that temperature for 2 hours. After carbonization, it was naturally cooled to room temperature. The obtained product was then boiled in 3mol / L hydrochloric acid solution for 4 hours and deionized water for 4 hours. It was then washed with deionized water until neutral and dried to obtain the coal-based carbon material, wherein the carbonization yield was 86%.

[0059] Example 2

[0060] Anthracite was crushed using a crusher, and then acid-washed with a 3 mol / L hydrochloric acid solution and alkaline-washed with a 3 mol / L sodium hydroxide solution to obtain pretreated anthracite.

[0061] 2g of pretreated anthracite and 10g of sodium chloride were mixed and placed in a ball mill and ball-milled in an oxygen-containing atmosphere (the ball mill speed was 400 rpm, the ball-to-material ratio was 10:1, the time was 12h, and the volume ratio of oxygen in the oxygen-containing atmosphere was 30%). After ball milling, the resulting mixture was washed with water to remove sodium chloride and dried to obtain anthracite precursor.

[0062] The obtained anthracite precursor was placed in a tube furnace and carbonized in a nitrogen atmosphere at a heating rate of 5℃ / min to 1200℃, and held at that temperature for 2 hours. After carbonization, it was naturally cooled to room temperature. The obtained product was then boiled in 3mol / L hydrochloric acid solution for 4 hours and deionized water for 4 hours. It was then washed with deionized water until neutral and dried to obtain the coal-based carbon material, wherein the carbonization yield was 81%.

[0063] Example 3

[0064] Anthracite was crushed using a crusher, and then acid-washed with a 3 mol / L hydrochloric acid solution and alkaline-washed with a 3 mol / L sodium hydroxide solution to obtain pretreated anthracite.

[0065] 10g of pretreated anthracite and 5g of sodium carbonate were mixed and placed in a ball mill and ball-milled in an oxygen-containing atmosphere (the ball mill speed was 800 rpm, the ball-to-material ratio was 30:1, the time was 24h, and the volume ratio of oxygen in the oxygen-containing atmosphere was 15%). After ball milling, the resulting mixture was washed with water to remove sodium carbonate and dried to obtain anthracite precursor.

[0066] The obtained anthracite precursor was placed in a tube furnace and carbonized in a nitrogen atmosphere at a heating rate of 2℃ / min to 1000℃, and held at that temperature for 2h. After carbonization, it was naturally cooled to room temperature. The obtained product was then boiled in 3mol / L hydrochloric acid solution for 4h and deionized water for 4h, and then washed with deionized water until neutral. After drying, the coal-based carbon material was obtained, with a carbonization yield of 80%.

[0067] Example 4

[0068] Bituminous coal is crushed using a crusher, and then acid-washed with a 3 mol / L hydrochloric acid solution and alkaline-washed with a 3 mol / L sodium hydroxide solution to obtain pretreated bituminous coal.

[0069] 10g of pretreated bituminous coal and 10g of sodium chloride were mixed and placed in a ball mill. The mixture was then ball-milled in an oxygen-containing atmosphere (the ball mill speed was 500 rpm, the ball-to-material ratio was 20:1, the time was 24 h, and the volume ratio of oxygen in the oxygen-containing atmosphere was 21%). After the ball milling was completed, the resulting mixture was washed with water to remove sodium chloride and dried to obtain anthracite precursor.

[0070] The obtained anthracite precursor was placed in a tube furnace and carbonized in a nitrogen atmosphere at a heating rate of 5℃ / min to 1400℃, and held at that temperature for 2 hours. After carbonization, it was naturally cooled to room temperature. The obtained product was then boiled in 3mol / L hydrochloric acid solution for 4 hours and deionized water for 4 hours. It was then washed with deionized water until neutral and dried to obtain the coal-based carbon material, wherein the carbonization yield was 68%.

[0071] Comparative Example 1

[0072] Anthracite was crushed using a crusher, and then acid-washed with a 3 mol / L hydrochloric acid solution and alkaline-washed with a 3 mol / L sodium hydroxide solution to obtain pretreated anthracite.

[0073] Pretreated anthracite was placed in a tubular furnace and carbonized in a nitrogen atmosphere at a heating rate of 5°C / min to 1200°C, and held at that temperature for 2 hours. After carbonization, it was naturally cooled to room temperature. The resulting product was then boiled in 3 mol / L hydrochloric acid solution for 4 hours and in deionized water for 4 hours. It was then washed with deionized water until neutral and dried to obtain the coal-based carbon material.

[0074] Comparative Example 2

[0075] Bituminous coal is crushed using a crusher, and then acid-washed with a 3 mol / L hydrochloric acid solution and alkaline-washed with a 3 mol / L sodium hydroxide solution to obtain pretreated bituminous coal.

[0076] The pretreated bituminous coal precursor was placed in a tubular furnace and carbonized in a nitrogen atmosphere at a heating rate of 5°C / min to 1400°C, and held at that temperature for 2 hours. After carbonization, it was naturally cooled to room temperature. The resulting product was then boiled in 3 mol / L hydrochloric acid solution for 4 hours and in deionized water for 4 hours. After washing with deionized water until neutral, it was dried to obtain the coal-based carbon material.

[0077] Performance testing

[0078] Test Example 1

[0079] The coal-based carbon material obtained in Example 1 was subjected to scanning electron microscopy (SEM) testing, and the resulting SEM images are shown below. Figure 1 As shown, from Figure 1 As can be seen, the coal-based carbon material obtained in this embodiment has a uniform particle size distribution and no obvious porous structure.

[0080] Test Example 2

[0081] The coal-based carbon material obtained in Example 1 was subjected to X-ray diffraction testing, and the resulting XRD pattern is shown below. Figure 2 As shown, from Figure 2 It can be seen that the (002) peak of the coal-based carbon material obtained in this embodiment has a large peak width, indicating that the graphitization degree is low, the disorder degree is high, the graphite interlayer spacing is large, and there are sufficient sodium storage sites.

[0082] The coal-based carbon material obtained in Comparative Example 1 was subjected to X-ray diffraction testing, and the resulting XRD pattern is shown below. Figure 3 As shown, from Figure 3 It can be seen that the peak width of the (002) peak of the coal-based carbon material obtained in Comparative Example 1 is small, indicating that the carbon material has a high degree of microcrystalline order, small interlayer spacing of graphite, and insufficient sodium storage sites.

[0083] Test Example 3

[0084] The coal-based carbon material obtained in Example 1 was subjected to transmission electron microscopy (HRTEM) testing, and the resulting HRTEM images are shown below. Figure 4As shown, from Figure 4 It can be seen that the coal-based carbon material obtained in this embodiment has a high degree of lattice disorder and a larger interlayer spacing, which is conducive to the interlayer insertion reaction of sodium ions and improves the sodium storage capacity of the platform at low potential.

[0085] The coal-based carbon material obtained in Comparative Example 1 was subjected to transmission electron microscopy (HRTEM) testing, and the resulting HRTEM images are shown below. Figure 5 As shown, from Figure 5 It can be seen that the lattice fringes of the coal-based carbon material obtained in Comparative Example 1 are ordered and regular, which is not conducive to the interlayer insertion reaction of sodium ions, resulting in poor sodium storage capacity of the platform at low potential.

[0086] Test Example 4

[0087] The coal-based carbon materials obtained in Examples 1-4 and Comparative Examples 1-2 were used as electrode materials to verify their electrochemical performance.

[0088] Coal-based carbon materials and sodium carboxymethyl cellulose were mixed at a mass ratio of 95:5, and an appropriate amount of water was added to obtain a slurry. The slurry was coated on copper foil and dried to obtain an electrode. In an argon-filled glove box, a sodium-ion battery was assembled with metallic sodium as the counter electrode, the obtained electrode as the working electrode, and a 1M NaClO4 solution (in which the solvent is EC+DEC+5%FEC) as the electrolyte. Electrochemical performance was then tested.

[0089] The obtained charge-discharge test curves are as follows Figures 6-11 As shown, where Figure 6 Example 1, Figure 7 Example 2, Figure 8 Example 3, Figure 9 Example 4, Figure 10 For Comparative Example 1, Figure 11 For comparative example 2, the test results are shown in Table 1:

[0090] Table 1. Electrochemical performance test results of coal-based carbon materials obtained in Examples 1-4 and Comparative Examples 1-2.

[0091] <![CDATA[Reversible specific capacity (mAh·g -1 )]]> First-time coulomb efficiency (%) Example 1 263 79 Example 2 332 82 Example 3 282 82 Example 4 304 81 Comparative Example 1 198 65 Comparative Example 2 241 73

[0092] The cycle performance curve of the sodium-ion battery corresponding to the anthracite-based carbon material obtained in Example 1 is as follows: Figure 12 As shown, from Figure 12 It can be seen that at a current rate of 0.2C, it has 298 mAh·g -1 It has a high reversible sodium storage capacity and retains 95.5% of its capacity after 100 cycles.

[0093] from Figures 6-12As can be seen from Table 1, the method provided by this invention can improve coal-based materials with poor sodium storage performance, and further improve the reversible specific capacity, first-cycle coulombic efficiency and cycle stability of coal-based carbon materials.

[0094] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative intent, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a coal-based carbon material, characterized in that, The steps are as follows: Coal and inorganic salts are mixed and ball-milled in an oxygen-containing atmosphere to remove the inorganic salts from the mixture, yielding a coal-based precursor. Before mixing, the coal is pretreated by sequentially crushing, acid washing, and alkali washing. The acid washing uses hydrochloric acid solution, and the alkali washing uses sodium hydroxide solution. The mass ratio of coal to inorganic salts is 1~10:1~10. The ball mill operates at a speed of 400-1000 rpm, a ball-to-material ratio of 5-30:1, and a time of 12-48 h. The coal-based precursor is carbonized to obtain the coal-based carbon material; the carbonization temperature is 800~1400℃, the heating rate is 0.5~10℃ / min, and the holding time is 0.5~5h; after the carbonization is completed, the obtained carbonization product is cooled, impurities are removed, water is washed and dried in sequence, and the cooling method is natural cooling to room temperature.

2. The preparation method according to claim 1, characterized in that, The coal includes one or more of anthracite, bituminous coal, sub-bituminous coal, and lignite.

3. The preparation method according to claim 1, characterized in that, The inorganic salts include water-soluble inorganic salts.

4. The preparation method according to claim 1, characterized in that, The oxygen volume fraction in the oxygen-containing atmosphere is 10-30%.

5. The preparation method according to claim 1, characterized in that, The carbonization is carried out in a protective atmosphere.

6. The coal-based carbon material prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The interlayer spacing of the coal-based carbon material is 0.370~0.376 nm.

7. The application of the coal-based carbon material according to claim 6 as a negative electrode material for sodium-ion batteries.

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