Method for preparing coal-based carbon material by finely regulating coal macromolecular structure and application of coal-based carbon material

Abstract

The invention discloses a method for preparing a coal-based carbon material by finely regulating and controlling a coal macromolecular structure and application of the coal-based carbon material, and belongs to the technical field of electrochemical energy storage. The method comprises the following steps: crushing and deliming raw material coal to obtain ultralow-ash-content coal powder; the method comprises the following steps: uniformly mixing ultralow-ash-content coal powder with extraction solvents with different polarities according to a certain proportion, weakening intermolecular interaction force by applying a certain condition, and enriching similar chemical components; pre-oxidizing the obtained pulverized coal, mixing the pre-oxidized pulverized coal with a catalyst and an additive in an organic solvent, and carrying out deep oxidation in an oxidizing atmosphere to promote directional conversion of hydroxyl generated by pre-oxidation to carboxyl; and transferring the carboxylated coal powder into a carbonization furnace, and carrying out high-temperature carbonization under the protection of inert gas to obtain the amorphous carbon material with high closed pore content. The coal-based carbon material prepared by the method shows rich closed pore content and excellent pore connectivity, obtains ultrahigh reversible specific capacity when being used as a sodium ion battery negative electrode, and is easy to realize large-scale preparation of the high-performance coal-based carbon material.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and particularly relates to a method for preparing coal-based carbon materials by finely regulating the macromolecular structure of coal and its application. Background Art

[0002] In recent years, the energy structure has been shifting from fossil fuels to clean and renewable energy sources. To address the limitations of the volatility and intermittency of renewable energy, there is an urgent need to develop a low-cost and efficient energy storage technology. Sodium-ion batteries have emerged as a rapidly developing direction in the energy storage field due to the abundant sodium resource reserves, excellent rate performance, and high safety performance. The anode material is a key component determining the energy density of the battery. Amorphous carbon anodes have become promising battery anode materials due to their high theoretical capacity, stable structure, and abundant precursor sources. The precursors of amorphous carbon are mainly divided into three categories: biomass, resin, and mineral. As a type of mineral, coal has the advantages of rich resources, low cost, and high carbon yield, making it an ideal precursor for carbon anodes. However, due to the complex macromolecular structure of coal, the pyrolysis process involves various types of chemical reactions, which is not conducive to the fine regulation of the structure of the derived carbon materials. In addition, coal has a high degree of polycyclic aromaticity, and direct carbonization will lead to the highly stacked carbon layers, which is not conducive to the storage of sodium ions. Recently, the research team of Professor Qiueshan Qiu from Dalian University of Technology used medium-rank bituminous coal as the raw material, obtained wash oil as the extraction solvent through high-temperature coking of coal, dissolved and removed the small molecular substances in the coal macromolecular structure that are prone to highly ordered arrangement. The amorphous carbon obtained after high-temperature carbonization exhibited a large interlayer spacing and a relatively rich pore structure, showing excellent cycle stability and rate performance in sodium-ion batteries (Carbon 162(2020)431-437). However, the obtained coal components are relatively complex and have a high aromaticity, and the structural changes during the carbonization process cannot be finely regulated, resulting in a too large specific surface area and a low initial efficiency. To counteract the ordered rearrangement of the high-aromaticity components of coal during carbonization, Researcher Luxiang Wang established a systematic mechanism for the formation of closed pores in coal-based carbon materials through an oxygen-driven carbon layer regulation strategy to inhibit excessive graphitization and promote the formation of closed pores during subsequent carbonization (Chem.Eng.J.493(2024)152389). However, the macromolecular structure of coal is very complex, and it is necessary to explore the evolution law of carbon microcrystals of various organic groups in coal during pre-oxidation and carbonization. Although CN 117401669A discloses a coal-based hard carbon material, its preparation method and application, physical separation of different macerals of coal by density gradient separation method, and combined with a suitable crosslinking method to inhibit the ordered arrangement of carbon layers during high-temperature pyrolysis, effectively improving the electrochemical performance of coal-based carbon anodes. However, the distribution range of the organic structure composition of the coal samples obtained by the physical separation method is still relatively wide, and it is expected to further refine the separation of coal components to achieve efficient regulation of the microcrystalline structure of coal-based carbon anodes. Summary of the Invention

[0003] In view of the problems such as the difficulty in suppressing the ordered arrangement of carbon layers during the carbonization process and the limited sodium ion storage performance caused by the complex macromolecular structure of coal, the present invention provides a method for preparing coal-based carbon materials by finely regulating the macromolecular structure of coal. The preparation method aims to enrich the organic group components with similar chemical structures in coal through the principle of like dissolves like, selectively convert the oxygen-containing functional groups introduced by pre-oxidation into carboxyl groups, use the three-dimensional cross-linked structure generated by the reaction of carboxyl groups with each other to inhibit the ordered arrangement of carbon microcrystals during carbonization, and promote the rapid adsorption and desorption of sodium ions with the carboxyl C=O group as the site. The coal-based carbon anode obtained by this preparation method has excellent reversible specific capacity and kinetic performance.

[0004] To solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A method for preparing coal-based carbon materials by finely regulating the macromolecular structure of coal, comprising the following steps:

[0006] Step 1, obtaining ultra-low ash coal powder by crushing and deashing the raw coal;

[0007] Step 2, uniformly mixing the ultra-low ash coal powder with extraction solvents of different polarities in a certain proportion, weakening the intermolecular interaction force by applying certain conditions and enriching similar chemical components, and distilling the obtained liquid to obtain soluble coal material;

[0008] Step 3, subjecting the soluble coal material to heat preservation pre-oxidation, cooling to room temperature, mixing the obtained pre-oxidation product with a catalyst and an additive in an organic solvent, and deeply oxidizing in an oxidizing atmosphere to promote the directional conversion of the hydroxyl groups generated by pre-oxidation into carboxyl groups;

[0009] Step 4, transferring the carboxylated coal powder to a carbonization furnace, and performing high-temperature carbonization under the protection of an inert gas to obtain an amorphous carbon material with a high closed pore content, namely the coal-based carbon material.

[0010] Further, the particle size of the ultra-low ash coal powder in the step 1 is ≤74 μm.

[0011] Further, the raw coal is one or several of lignite, bituminous coal, anthracite or macerals in different raw coals (including inertinite, vitrinite, exinite), etc.

[0012] Further, the deashing in the step 1 is specifically washing and deashing with acid solutions of different types and concentrations, and the acid solution is one or several of hydrochloric acid, hydrofluoric acid, sulfuric acid or nitric acid, and the concentration is 0.5-10 mol / L.

[0013] Further, the extraction solvents with different polarities in step 2 are one or more of tetrahydrofuran, 1-methyl-2-pyrrolidone, n-hexane, carbon disulfide, benzene, chloroform, dichloromethane, and pyridine.

[0014] Further, the specific treatment conditions for weakening the intermolecular interaction force and enriching similar chemical components in step 2 are that the heating temperature is 50-100 °C or the ultrasonic frequency is 20-200 kHz, and the treatment time is 0.5-24 h.

[0015] Further, the oxidation atmosphere for heat preservation and pre-oxidation in step 3 includes oxygen or air, the gas flow rate is 50-500 m 3 / h, the temperature of the muffle furnace is 100-500 °C, and the heat preservation time is 0.5-24 h.

[0016] Further, the catalyst in step 3 includes one or more of iron nitrate, iron chloride, iron sulfate, and 2,2,6,6-tetramethylpiperidine oxide, and the additive is one or more of sodium chloride, potassium chloride, or other metal salts. The mass ratio of the pre-oxidation product, catalyst, and additive is 5:5:1-5:20:2.

[0017] Further, the reaction time for deep oxidation in the oxidation atmosphere in step 3 is 0.5-24 h. The rotation speed of the centrifuge in step 3 is 1000-10000 rad / min, and the centrifugation time is 3-60 min.

[0018] Further, high-temperature carbonization is carried out under the protection of an inert gas in step 4. The inert atmosphere is one of argon or nitrogen. The carbonization temperature is 800-1500 °C, the heating rate is 0.5-10 °C / min, and the heat preservation time is 0.5-6 h.

[0019] The closed pore average pore diameter of the coal-based carbon material is 0.3-2 nm, the pore connectivity parameter f a is 0.5-1.2, the pore spacing is 7-4 nm, the carbon yield is 30-50 wt.%, and the ash content is ≤0.5 wt.%.

[0020] The application of the coal-based carbon material in the negative electrode of an ion battery can be used for the negative electrode of a sodium-ion battery or the negative electrode of a lithium / potassium ion battery.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This project finely separates coal raw materials through chemical methods. Based on the principle of "like dissolves like", different polar organic solvents are used to separate the components with specific molecular structures in coal, achieving dimensionality reduction of complex macromolecular structures. The oxygen-containing functional groups introduced by pre-oxidation are deeply oxidized into carboxyl functional groups. The strong cross-linked structure between carboxyl groups inhibits the rearrangement of the carbon layer, and the carboxyl C=O groups can provide more active sites for sodium ion adsorption. The coal-based carbon materials with finely regulated coal macromolecular structures prepared have a high closed pore content, good pore connectivity, and abundant sodium ion adsorption sites, thus showing more excellent electrochemical performance.

[0023] 2. The coal-based carbon materials with finely regulated coal macromolecular structures of the present invention have a developed pore structure, which can provide more storage sites and diffusion channels for alkali metal ions, showing a high initial Coulomb efficiency, high capacity, and good cycle stability. For example, the reversible capacity of lithium-ion batteries can reach up to 400 - 700 mAh / g at most, the reversible capacity of sodium-ion batteries reaches 300 - 400 mAh / g, and the reversible capacity of potassium-ion batteries is as high as 300 - 350 mAh / g.

[0024] 3. The preparation method of the present invention has the characteristics of rich raw material resources, low cost, high carbon yield, and simple process, and is easy to achieve large-scale preparation. While realizing the efficient utilization of coal resources, it can create high economic value and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 Infrared spectra of the refined coal raw materials prepared in Example 1 and the untreated coal raw materials.

[0027] Figure 2 X-ray diffraction spectra of the refined coal-based carbon materials prepared in Example 1 and the untreated coal-based carbon materials.

[0028] Figure 3 Charge-discharge curves of the refined coal-based carbon materials prepared in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To deeply understand the present invention, we will describe it comprehensively and meticulously. However, the present invention has multiple implementation manners and is not limited to the specific examples listed herein. The presentation of these examples aims to deepen the comprehensive understanding of the disclosed content of the present invention.

[0030] Example 1

[0031] Step 1: Place 100 g of bituminous coal in a pulverizer, pulverize it, and sieve it through a 200-mesh sieve to obtain pulverized coal with a particle size ≤ 74 μm.

[0032] Step 2: Place the above-mentioned pulverized coal in a beaker, add 250 mL of hydrochloric acid solution with a concentration of 5 mol / L, heat it in a water bath at 75 °C and stir for 12 h, then perform suction filtration to remove the metal salt ash in the coal; add 250 mL of 40% hydrofluoric acid solution, heat it in a water bath at 75 °C and stir for 12 h, perform suction filtration to remove the silicate ash in the coal, wash it with deionized water until neutral, and dry it to obtain low-ash coal.

[0033] Step 3: Take 20 g of low-ash coal and place it in a beaker, take 500 mL of tetrahydrofuran solution, put it in an ultrasonic machine and ultrasonicate it at a frequency of 40 kHz for 6 h; transfer the mixed liquid to a centrifuge tube and centrifuge it at a speed of 8000 rad / min for 10 min; transfer the supernatant to a round-bottom flask and distill it to obtain soluble coal material.

[0034] Step 4: Place the soluble coal material obtained in Step 3 in a muffle furnace, under an air atmosphere, heat it at a heating rate of 1 °C / min to 300 °C, keep it warm for 2 h, and then cool it to room temperature. Place 5 g of the obtained product, 5 g of 2,2,6,6-tetramethylpiperidine oxide, 10 g of iron nitrate, and 2 g of potassium chloride together in 200 mL of 1,2-dichloroethane, perform re-oxidation under an air atmosphere, centrifuge at a speed of 8000 rad / min to obtain a precipitate, and dry it to obtain a coal precursor with fine-tuned molecular structure.

[0035] Step 5: Heat the coal precursor with fine-tuned molecular structure obtained in Step 4 under an argon atmosphere at a heating rate of 2 °C / min to 1300 °C and keep it warm for 2 h to obtain a refined coal-based carbon material.

[0036] The carbon yield of the refined coal-based carbon material prepared in Example 1 is 40 wt.%, the ash content is 0.12 wt.%, the average pore diameter is 0.410 nm, and the pore connectivity parameter is 0.82. Mix the prepared refined coal-based carbon material powder, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 80:10:10 to form a slurry, uniformly scrape the slurry onto a current collector copper foil, and after drying, cut it into electrode sheets. The battery is assembled in a glove box under an argon atmosphere, using metallic sodium as the counter electrode and 1 M NaPF 6 (bis(2-methoxyethyl) ether) solution as the electrolyte to assemble a CR2032 coin cell. After testing, the hard carbon negative electrode has a reversible specific capacity of 320.5 mAh / g at a current density of 30 mA / g, and the first Coulombic efficiency is 87%.

[0037] Example 2

[0038] The difference between this embodiment and Embodiment 1 is that the raw coal used in Step 1 is anthracite and the current density is 20 mA / g. Other steps and parameters are the same as those in Embodiment 1.

[0039] Step 1: Place 100 g of anthracite in a pulverizer, pulverize it, and sieve it through a 200-mesh sieve to obtain coal powder with a particle size ≤ 74 μm.

[0040] Step 2: Place the above coal powder in a beaker, add 250 mL of hydrochloric acid solution with a concentration of 5 mol / L, heat it in a water bath at 75 °C and stir for 12 h, then filter by suction to remove the metal salt ash in the coal; add 250 mL of 40% hydrofluoric acid solution, heat it in a water bath at 75 °C and stir for 12 h, filter by suction to remove the silicate ash in the coal, wash it with deionized water until neutral, and dry it to obtain low-ash coal.

[0041] Step 3: Take 20 g of low-ash coal and place it in a beaker, take 500 mL of tetrahydrofuran solution, put it in an ultrasonic machine and ultrasonic it at a frequency of 40 kHz for 6 h; transfer the mixed liquid to a centrifuge tube and centrifuge it at a speed of 8000 rad / min for 10 min; transfer the supernatant to a round-bottom flask and distill it to obtain soluble coal material.

[0042] Step 4: Place the soluble coal material obtained in Step 3 in a muffle furnace. Under an air atmosphere, heat it at a heating rate of 1 °C / min to 300 °C, keep it warm for 2 h, and then cool it to room temperature. Place 5 g of the obtained product together with 5 g of 2,2,6,6-tetramethylpiperidine oxide, 10 g of iron nitrate, and 2 g of potassium chloride in 200 mL of 1,2-dichloroethane, and perform re-oxidation under an air atmosphere. Centrifuge at a speed of 8000 rad / min to obtain a precipitate, and after drying, obtain a coal precursor with fine-tuned molecular structure.

[0043] Step 5: Heat the coal precursor with fine-tuned molecular structure obtained in Step 4 under an argon atmosphere at a heating rate of 2 °C / min to 1300 °C, and keep it warm for 2 h to obtain a refined coal-based carbon material.

[0044] The carbon yield of the refined coal-based carbon material prepared in Embodiment 2 is 46 wt.%, the ash content is 0.24 wt.%, the average pore diameter is 0.483 nm, and the pore connectivity parameter is 0.73. Mix the prepared refined coal-based carbon material powder with conductive carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10 to form a slurry. Uniformly scrape the slurry onto a current collector copper foil, and after drying, cut it into electrode sheets. The battery is assembled in a glove box under an argon atmosphere, using metallic sodium as the counter electrode and 1 M NaPF 6Using a solution of diethylene glycol dimethyl ether as the electrolyte, a CR2032 button cell was assembled. After testing, the hard carbon negative electrode had a reversible specific capacity of 343.6 mAh / g at a current density of 20 mA / g, and the initial Coulombic efficiency was 87%.

[0045] Example 3

[0046] The difference between this example and Example 1 is that the solvent used in Step 3 was 1-methyl-2-pyrrolidone. The other steps and parameters were the same as in Example 1.

[0047] In Step 1, 100 g of bituminous coal was placed in a pulverizer and pulverized, and then passed through a 200-mesh sieve to obtain coal powder with a particle size ≤ 74 μm.

[0048] In Step 2, the above-mentioned coal powder was placed in a beaker, 250 mL of a hydrochloric acid solution with a concentration of 5 mol / L was added, and it was heated and stirred in a water bath at 75 °C for 12 h, then filtered by suction to remove the metal salt ash in the coal; 250 mL of 40% hydrofluoric acid solution was added, and it was heated and stirred in a water bath at 75 °C for 12 h, then filtered by suction to remove the silicate ash in the coal, and washed with deionized water until neutral, and dried to obtain low-ash coal.

[0049] In Step 3, 20 g of low-ash coal was placed in a beaker, 500 mL of 1-methyl-2-pyrrolidone solution was taken, and it was ultrasonicated in an ultrasonic machine at a frequency of 40 kHz for 6 h; the mixed liquid was transferred to a centrifuge tube and centrifuged at a speed of 8000 rad / min for 10 min; the supernatant was transferred to a round-bottom flask and distilled to obtain soluble coal material.

[0050] In Step 4, the soluble coal material obtained in Step 3 was placed in a muffle furnace, and under an air atmosphere, it was heated at a heating rate of 1 °C / min to 300 °C, held for 2 h, and then cooled to room temperature. 5 g of the obtained product, 5 g of 2,2,6,6-tetramethylpiperidine oxide, 10 g of iron nitrate, and 2 g of potassium chloride were placed together in 200 mL of 1,2-dichloroethane, and re-oxidation was carried out under an air atmosphere. The precipitate was obtained by centrifugation at a speed of 8000 rad / min and dried to obtain a coal precursor with fine-tuned molecular structure.

[0051] In Step 5, the coal precursor with fine-tuned molecular structure obtained in Step 4 was heated to 1300 °C at a heating rate of 2 °C / min under an argon atmosphere and held for 2 h to obtain a refined coal-based carbon material.

[0052] The carbon yield of the refined coal-based carbon material prepared in Example 3 is 47 wt.%, the ash content is 0.18 wt.%, the average pore diameter is 0.532 nm, and the pore connectivity parameter is 0.73. The prepared refined coal-based carbon material powder is mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10 to form a slurry. The slurry is evenly spread on the current collector copper foil, dried, and then the electrode sheet is cut. The battery is assembled in a glove box under an argon atmosphere, using metallic sodium as the counter electrode and 1M NaPF 6 (bis(2-methoxyethyl) ether) solution as the electrolyte to assemble a CR2032 button cell. After testing, the hard carbon negative electrode has a reversible specific capacity of 310.4 mAh / g at a current density of 30 mA / g, and the first Coulombic efficiency is 86%.

[0053] Example 4

[0054] The difference between this example and Example 1 is that the extraction conditions used in Step 3 are heating to 60 °C and a current density of 20 mA / g. Other steps and parameters are the same as those in Example 1.

[0055] Step 1: Place 100 g of bituminous coal in a pulverizer, pulverize it, and pass it through a 200-mesh sieve to obtain coal powder with a particle size ≤ 74 μm.

[0056] Step 2: Place the above coal powder in a beaker, add 250 mL of hydrochloric acid solution with a concentration of 5 mol / L, heat it in a water bath at 75 °C and stir for 12 h, then filter by suction to remove the metal salt ash in the coal; add 250 mL of 40% hydrofluoric acid solution, heat it in a water bath at 75 °C and stir for 12 h, then filter by suction to remove the silicate ash in the coal, and wash it with deionized water until neutral, and dry it to obtain low-ash coal.

[0057] Step 3: Take 20 g of low-ash coal and place it in a beaker, take 500 mL of tetrahydrofuran solution, put it in a water bath and stir at a constant temperature of 60 °C for 6 h; transfer the mixed liquid to a centrifuge tube and centrifuge at a speed of 8000 rad / min for 10 min; transfer the supernatant to a round-bottom flask and distill it to obtain soluble coal material.

[0058] Step 4: Place the soluble coal material obtained in Step 3 in a muffle furnace, under an air atmosphere, with a heating rate of 1 °C / min, heat it to 300 °C, hold it for 2 h, and then cool it to room temperature. Place 5 g of the obtained product together with 5 g of 2,2,6,6-tetramethylpiperidine oxide, 10 g of iron nitrate, and 2 g of potassium chloride in 200 mL of 1,2-dichloroethane, and perform reoxidation under an air atmosphere. Centrifuge at a speed of 8000 rad / min to obtain a precipitate, and dry it to obtain a coal precursor with fine-tuned molecular structure.

[0059] (5) The molecular structure finely regulated coal precursor obtained in step (4) is heated to 1300 °C at a heating rate of 2 °C / min under an argon atmosphere and held for 2 h to obtain a refined coal-based carbon material.

[0060] The carbon yield of the refined coal-based carbon material prepared in Example 5 is 41 wt.%, the ash content is 0.13 wt.%, the average pore diameter is 0.431 nm, and the pore connectivity parameter is 0.86. The prepared refined coal-based carbon material powder is mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10 to form a slurry. The slurry is evenly coated on a current collector copper foil, dried, and then cut into electrode sheets. The battery is assembled in a glove box under an argon atmosphere, using metallic sodium as the counter electrode and a 1M NaPF 6 (bis(2-methoxyethyl) ether) solution as the electrolyte to assemble a CR2032 coin cell. After testing, the hard carbon negative electrode has a reversible specific capacity of 359.5 mAh / g at a current density of 20 mA / g, and the first Coulombic efficiency is 89%.

[0061] Example 5

[0062] The difference between this example and Example 1 is that the additive used in step (4) is sodium chloride. Other steps and parameters are the same as those in Example 1.

[0063] (1) 100 g of bituminous coal is placed in a pulverizer and pulverized, and then passed through a 200-mesh sieve to obtain coal powder with a particle size ≤ 74 μm.

[0064] (2) The above-mentioned coal powder is placed in a beaker, 250 mL of hydrochloric acid solution with a concentration of 5 mol / L is added, and it is heated and stirred in a water bath at 75 °C for 12 h, then filtered by suction to remove the metal salt ash in the coal; 250 mL of 40% hydrofluoric acid solution is added, and it is heated and stirred in a water bath at 75 °C for 12 h, then filtered by suction to remove the silicate ash in the coal, and washed with deionized water until neutral, and then dried to obtain low-ash coal.

[0065] (3) Take 20 g of low-ash coal and place it in a beaker, take 500 mL of tetrahydrofuran solution, and ultrasonicate it in an ultrasonic machine at a frequency of 40 kHz for 6 h; transfer the mixed liquid to a centrifuge tube and centrifuge it at a speed of 8000 rad / min for 10 min; transfer the supernatant to a round-bottom flask and distill it to obtain soluble coal material.

[0066] (4) Place the soluble coal material obtained in step (3) in a muffle furnace. Under an air atmosphere, heat it at a heating rate of 1 °C / min to 300 °C, hold for 2 h, and then cool to room temperature. Place 5 g of the obtained product together with 5 g of 2,2,6,6-tetramethylpiperidine oxide, 10 g of iron nitrate, and 2 g of sodium chloride in 200 mL of 1,2-dichloroethane, and conduct re-oxidation under an air atmosphere. Centrifuge at a speed of 8000 rad / min to obtain a precipitate, and after drying, obtain a coal precursor with fine-tuned molecular structure.

[0067] (5) Heat the coal precursor with fine-tuned molecular structure obtained in step (4) to 1300 °C at a heating rate of 2 °C / min under an argon atmosphere, and hold for 2 h to obtain a refined coal-based carbon material.

[0068] The carbon yield of the refined coal-based carbon material prepared in Example 5 is 41 wt.%, the ash content is 0.15 wt.%, the average pore diameter is 0.489 nm, and the pore connectivity parameter is 0.69. Mix the prepared refined coal-based carbon material powder with conductive carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10 to form a slurry. Spread the slurry evenly on the current collector copper foil, and after drying, cut it into electrode sheets. The battery is assembled in a glove box under an argon atmosphere, using metallic sodium as the counter electrode and a 1M NaPF 6 (bis(2-methoxyethyl) ether) solution as the electrolyte to assemble a CR2032 coin cell. After testing, the hard carbon negative electrode has a reversible specific capacity of 315.3 mAh / g at a current density of 30 mA / g, and the first Coulombic efficiency is 86%.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 1 is that in step (3) of Comparative Example 1, an extraction solvent is not used. Other steps and parameters of Comparative Example 1 are the same as those of Example 1.

[0071] Mix the coal-based carbon material prepared in Comparative Example 1 with carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10 to form a slurry, and then spread the slurry evenly on the current collector copper foil. After drying, cut it into electrode sheets. The battery is assembled in a glove box under an argon atmosphere, using metallic sodium as the counter electrode and a 1M NaPF6 (bis(2-methoxyethyl) ether) solution as the electrolyte to assemble a CR2032 coin cell. After testing, the hard carbon negative electrode has a reversible specific capacity of 262.1 mAh / g at a current density of 30 mA / g, and the first Coulombic efficiency is 78%.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 1 is that in step (4) of Comparative Example 1, catalytic oxidation is not carried out. Other steps and parameters of Comparative Example 2 are the same as those of Example 1.

[0074] The coal-based carbon material prepared in Comparative Example 2 was mixed with carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10 to form a slurry. Then, the slurry was evenly spread on a current collector copper foil. After drying, the electrode was cut. The battery was assembled in a glove box under an argon atmosphere, using metallic sodium as the counter electrode and a 1M NaPF 6 (bis(2-methoxyethyl) ether) solution as the electrolyte to assemble a CR2032 button cell. After testing, the hard carbon negative electrode had a reversible specific capacity of 231.5 mAh / g at a current density of 30 mA / g, and the first Coulombic efficiency was 68%.

[0075] Figure 1 Infrared spectra of the refined coal raw materials prepared in Example 1 and the untreated coal raw materials. In the spectra, the aliphatic CH -1 symmetric stretching vibration at around 2848 cm 2 and the aliphatic CH -1 symmetric stretching vibration at around 2863 cm 3 and the aliphatic CH -1 antisymmetric stretching vibration at around 2922 cm 2 and the aliphatic CH -1 symmetric stretching vibration at around 2954 cm 2 were observed. After treatment, the peak intensity in the range of 3000 - 2800 cm -1 increased significantly, indicating an increase in the content of aliphatic chains in the precursor.

[0076] Figure 2 X-ray diffraction spectra of the refined coal-based carbon materials prepared in Example 1 and the untreated coal-based carbon materials. It can be seen that the diffraction peak corresponding to the (002) crystal plane of the coal with fine molecular structure regulation shifted to the left, corresponding to an increase in the interlayer spacing of the carbon microcrystals. Figure 1 It can be seen that the diffraction peak corresponding to the (002) crystal plane of the coal with fine molecular structure regulation shifted to the left, corresponding to an increase in the interlayer spacing of the carbon microcrystals.

[0077] Figure 3 Charge-discharge curves of the coal-based carbon materials prepared in Example 1. It can be seen that the carbon materials prepared from the coal with fine molecular structure regulation exhibited excellent electrochemical performance. At a current density of 30 mA / g, the reversible capacity of the sample was 320.5 mAh / g, and the first Coulombic efficiency was 87%.

[0078] The content not detailed in the description of the present invention belongs to the prior art well-known to those skilled in the art. Although the illustrative specific embodiments of the present invention have been described above for the understanding of those skilled in the art in this technical field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those ordinary skilled in the art in this technical field, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

Claims

1. A method for preparing coal-based carbon materials by finely regulating the macromolecular structure of coal, characterized in that: The following steps are involved: Step 1, obtaining ultra-low ash coal powder by crushing and deashing raw coal; Step 2, uniformly mixing the ultra-low ash coal powder and extraction solvents with different polarities in a certain proportion, applying certain conditions to weaken the intermolecular interaction and enrich similar chemical components, and distilling the resulting liquid to obtain soluble coal material; Step 3, pre-oxidizing the soluble coal material by heat preservation, cooling to room temperature, mixing the obtained pre-oxidation product with a catalyst and an additive in an organic solvent, and deeply oxidizing it under an oxidizing atmosphere to promote the directional conversion of the hydroxyl group generated by the pre-oxidation to a carboxyl group; Step 4, transferring the carboxylated coal powder to a carbonization furnace, and performing high-temperature carbonization under the protection of an inert gas to obtain an amorphous carbon material with a high closed-pore content, namely, a coal-based carbon material.

2. The method for preparing coal-based carbon materials by finely controlling the coal macromolecular structure according to claim 1, characterized in that: The particle size of the ultra-low ash coal powder in step 1 is ≤74 μm. The deashing in step 1 is specifically performed by washing and deashing with acid solutions of different types and concentrations, wherein the acid solution is one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid or nitric acid, and the concentration is 0.5-10 mol / L.

3. The method for preparing coal-based carbon materials by finely controlling the coal macromolecular structure according to claim 1, characterized in that: The extraction solvents of different polarities in step 2 are one or more of tetrahydrofuran, 1-methyl-2-pyrrolidone, n-hexane, carbon disulfide, benzene, chloroform, dichloromethane, and pyridine.

4. The method for preparing coal-based carbon materials by finely controlling the coal macromolecular structure according to claim 1, characterized in that: The specific treatment conditions for weakening the intermolecular interaction force and enriching similar chemical components by applying certain conditions in step 2 are heating temperature of 50-100° C. or ultrasonic frequency of 20-200 kHz and treatment time of 0.5-24 h.

5. The method for preparing coal-based carbon materials by finely controlling the coal macromolecular structure according to claim 1, characterized in that: The oxidizing atmosphere for the heat preservation pre-oxidation in step 3 includes oxygen or air, and the gas flow rate is 50 to 500 m / s. 3 / h, the muffle furnace temperature is 100~500℃, and the holding time is 0.5~24h.

6. The method for preparing coal-based carbon materials by finely controlling the coal macromolecular structure according to claim 1, characterized in that: In step 3, the catalyst includes one or more of ferric nitrate, ferric chloride, ferric sulfate, and 2,2,6,6-tetramethylpiperidinyl oxide, and the additive is one or more of sodium chloride or potassium chloride; the mass ratio of the pre-oxidation product, the catalyst and the additive is 5:5:1 to 5:20:

2.

7. The method for preparing coal-based carbon materials by finely controlling the coal macromolecular structure according to claim 1, characterized in that: The reaction time of deep oxidation in the oxidizing atmosphere in step 3 is 0.5 to 24 hours.

8. The method for preparing coal-based carbon materials by finely controlling the macromolecular structure of coal according to claim 1, characterized in that: In step 4, high-temperature carbonization is performed under the protection of an inert gas, the inert atmosphere is one of argon or nitrogen, the carbonization temperature is 800-1500° C., the heating rate is 0.5-10° C. / min, and the insulation time is 0.5-6h.

9. The coal-based carbon material prepared by the method according to any one of claims 1 to 8 is used as the negative electrode of an ion battery, characterized in that: The coal-based carbon material has an average closed pore diameter of 0.3 to 2 nm and a pore connectivity parameter f a The pore spacing is 0.5-1.2, the pore spacing is 7-4 nm, the carbon yield is 30-50 wt.%, and the ash content is ≤0.5 wt.%.

10. Use of the coal-based carbon material prepared by the method according to any one of claims 1 to 8 in the negative electrode of an ion battery.

Images