Method for preparing coal-based hard carbon by enhancing coal oxidation reaction activity

Abstract

The invention discloses a method for preparing coal-based hard carbon by enhancing coal oxidation reaction activity, and belongs to the technical field of electrochemical energy storage. The preparation method comprises the following steps: crushing and deliming raw material coal to obtain ultra-pure coal powder; the method comprises the following steps: mixing ultra-pure coal powder with an oxygen-containing organic solvent, removing reaction inert components in the ultra-pure coal powder, uniformly mixing the ultra-pure coal powder with a hydrogen-donating reagent, carrying out co-heat treatment, and attacking and destroying an aromatic ring conjugated structure in coal molecules by using hydrogen free radicals released by heating the hydrogen-donating reagent, so as to prepare the coal powder with high oxidation reaction activity; performing oxidation crosslinking on the coal powder with high oxidation reaction activity to obtain oxygen-enriched coal powder; and performing high-temperature carbonization in an inert gas atmosphere to obtain the hard carbon material with developed closed pores. The coal-based hard carbon prepared by the method shows a rich ultra-microporous structure, is thin in pore wall and high in pore connectivity, obtains high reversible specific capacity and excellent dynamic performance as a sodium ion battery negative electrode, and can realize industrial production and commercial application of high-capacity coal-based hard carbon.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage, and particularly relates to a method for preparing coal-based hard carbon by enhancing coal oxidation reaction activity. BACKGROUND

[0002] With the acceleration of global energy transformation and the booming development of the electric vehicle market, the demand for efficient, environmentally friendly and cost-controllable energy storage systems is increasingly urgent. Sodium-ion batteries are attracting attention due to their abundant raw materials, excellent electrochemical performance, and high safety performance. As a key component of sodium-ion batteries, the negative electrode material greatly affects the overall performance of sodium-ion batteries. Hard carbon material has become the most promising negative electrode material for sodium-ion batteries due to its high sodium storage capacity, stable structure, and appropriate redox potential. As a key raw material for preparing hard carbon, carbonaceous precursors have an important influence on the microcrystalline structure, pore structure and surface chemistry of hard carbon. Coal, as a high-quality carbon source, has the advantages of abundant resources, low cost, high carbon yield and adjustable structure, and has become an ideal carbonaceous precursor for preparing hard carbon. However, the high aromaticity of coal has a strong π-π conjugation effect, which causes the carbon layers to be highly ordered after direct carbonization, thereby affecting the performance of the final hard carbon product. The pre-oxidation method, as a widely used strategy for structure regulation of coal-based hard carbon, can introduce oxygen-containing cross-linking structures into the coal molecular structure, thereby hindering the melting and rearrangement of aromatic structures in coal.

[0003] Recently, CN119873790A discloses a long-flame coal-based hard carbon negative material, a preparation method and a secondary battery. Through the synergistic oxidation of supercritical water and dissolved oxygen, the intensity and uniformity of the oxidation reaction on the surface of coal particles are enhanced, and more ion storage sites and transmission channels can be formed after carbonization, thereby improving the sodium storage performance of the coal-based hard carbon. However, due to the complexity of coal components, there are significant differences in the oxidation reaction activity between these components, which hinders the efficient application of the pre-oxidation strategy. CN117401669A discloses a coal-based hard carbon material, a preparation method and an application thereof. By using a physical separation method, the vitrinite group with high oxidation reaction activity in coal is sorted out, and a hard carbon with excellent sodium storage performance is prepared after pre-oxidation and carbonization. However, this method cannot further separate the organic macromolecules in coal, limiting the improvement of the oxidation activity of the coal precursor. CN115535996B discloses an effective segmentation of complex components of asphalt, which is also a complex organic mixture, after four-component analysis. Through further pre-oxidation strategy, differential cross-linked asphalt is obtained. During the subsequent carbonization process, these oxygen-containing functional groups promote the formation of disordered carbon layer structure, which ultimately improves the electrochemical performance of the material as a negative electrode for alkali metal ion batteries.

[0004] However, there is still a lack of regulation strategies targeting the improvement of the oxidation reaction activity of coal precursors, which makes it difficult to introduce a large number of oxygen-containing functional groups uniformly in the pre-oxidation process of coal precursors, thereby becoming a key bottleneck restricting the development of high-performance coal-based hard carbon. SUMMARY

[0005] In view of the problem of uneven oxidation reactivity of coal components in the pre-oxidation process, the present application provides a method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal. The method aims to enrich and remove the chemically inert components in coal by chemical dissolution. Then the obtained coal powder is co-treated with a hydrogen-donating organic reagent to release hydrogen radicals to destroy the aromatic ring structure of coal and strengthen its oxidation reaction activity. Based on this, in the subsequent oxidation process, the cross-linked structure can be uniformly constructed in the bulk phase of coal, effectively inhibiting the excessive rearrangement of carbon sheets during high-temperature carbonization. At the same time, the highly interconnected pore structure surrounded by disordered carbon layers can serve as a storage site for alkali metal ions, achieving high-capacity storage. The coal-based carbon negative electrode obtained by the preparation method has high reversible specific capacity and excellent rate performance.

[0006] To solve the above technical problems, the application adopts the following technical solutions:

[0007] A method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal, comprising the following steps:

[0008] Step 1, crushing and deashing the raw coal to obtain ultra-pure coal powder;

[0009] Step 2, uniformly mixing the ultra-pure coal powder with an oxygen-containing organic solvent, after heat preservation and stirring, dissolving and removing the chemically inert components in the coal, taking the precipitate after centrifugation, washing with water and drying to obtain the treated coal powder;

[0010] Step 3, heat treating the treated coal powder with a hydrogen-donating organic reagent, using the hydrogen radicals released by the hydrogen-donating reagent to attack and destroy the aromatic ring structure with strong conjugation in the coal molecules, then cooling to room temperature to obtain high-oxidation-reaction-activity coal powder;

[0011] Step 4, oxidizing and cross-linking the high-oxidation-reaction-activity coal powder by a pre-oxidation method to obtain oxygen-rich coal powder;

[0012] Step 5, high-temperature carbonization of the oxygen-rich coal powder under the protection of inert gas to obtain amorphous carbon material with highly disordered microcrystalline structure, i.e. coal-based hard carbon.

[0013] Further, the deashing in step 1 is washing with acid solutions of different types and concentrations, the acid solutions include one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid or nitric acid, with a concentration of 0.1-10 mol / L; the particle size of the ultra-pure coal powder after deashing is ≤100 μm, and the ash content is 0.1-1.0 wt.%.

[0014] Further, the oxygen-containing organic solvent is one or more of 1-methyl-2-pyrrolidone, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran, diethyl ether, and isopropyl alcohol, and the ratio of the oxygen-containing organic solvent to the ultra-pure coal powder is 5:1 to 50:1.

[0015] Further, the hydrogen-donating organic reagent includes one or more of o-diphenol, p-diphenol, sorbitol, butyl-tertiary-orthophenol, glycine, and sodium glutamate.

[0016] Further, the temperature for the incubation and stirring in step 2 is 30 to 120°C, and the incubation time is 0.5 to 24 h.

[0017] Further, the temperature for the incubation and stirring in step 3 is 30 to 200°C, and the incubation time is 0.5 to 24 h.

[0018] Further, the high-oxidation reactivity coal powder is oxidized and crosslinked by a pre-oxidation method in step 4 to obtain oxygen-rich coal powder, which is specifically:

[0019] The pre-oxidation method is gas-phase pre-oxidation, liquid-phase pre-oxidation, or solid-phase pre-oxidation.

[0020] The conditions for the gas-phase pre-oxidation are that the oxidation atmosphere for the incubation and pre-oxidation includes oxygen or air, the gas flow rate is 50 to 500 m³ / h, the muffle furnace temperature is 100 to 500°C, and the incubation time is 0.5 to 24 h.

[0021] The conditions for the liquid-phase pre-oxidation are that the oxidizing agent is one or more of hydrogen peroxide, sodium hypochlorite, ammonium persulfate, and sulfuric acid, the mass ratio of the oxidizing agent to the coal is 0.5:1 to 5:1, the reaction temperature is 30 to 80°C, and the reaction time is 4 to 24 h.

[0022] The conditions for the solid-phase pre-oxidation are that the oxidizing agent is one or more of manganese dioxide, potassium permanganate, sodium nitrite, and potassium dichromate, the mass ratio of the oxidizing agent to the coal is 0.1:1 to 2:1, the reaction temperature is 80 to 300°C, and the reaction time is 0.5 to 5 h.

[0023] Further, the high-temperature carbonization under inert gas protection in step 5 is specifically that the inert gas is one of argon or nitrogen, the temperature for the high-temperature carbonization is 800 to 1500°C, the temperature rising rate is 0.5 to 10°C / min, and the incubation time is 0.5 to 6 h.

[0024] Coal-based carbon material in an ion battery negative electrode, the oxygen content of the oxygen-rich coal powder is 25-40 wt.%, the closed pore average pore diameter of the coal-based hard carbon is 0.3-2 nm, the average pore wall thickness is 0.3-1 nm, the pore spacing is 2-8 nm, the pore wall carbon layer curvature is 0.2-0.4, and the interlayer spacing is 0.37-0.40 nm.

[0025] Application of coal-based carbon material in a sodium ion battery, a lithium ion battery or a potassium ion battery negative electrode.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] 1. The present application improves the reactivity of coal precursors through a "component screening-hydrogenation reaction" coupling strategy. First, a high-dipole-moment oxygen-containing organic solvent is used to generate an orientation force similar to the electron cloud of the chemically inert components in the coal, effectively removing the chemically inert components in the coal. Further, the hydrogen donor reagent is co-heat treated with the obtained coal powder, and the hydrogen radicals released by the heated hydrogen donor reagent attack the macromolecular aromatic ring structure of the coal, destroying its strong π-π conjugation effect, realizing the conversion of aromatic carbon to aliphatic carbon, and further strengthening its oxidation reactivity.

[0028] 2. The high reactivity of the coal precursor in the present application promotes the construction of a rich and uniform three-dimensional cross-linked structure in its bulk phase during the pre-oxidation process. This three-dimensional cross-linked structure not only stabilizes the aromatic nucleus in the coal molecules, but also hinders their melting rearrangement. Ultimately, it promotes the growth of large-curvature carbon sheet layers and forms ultramicropores with small pore spacing and good connectivity.

[0029] 3. The preparation method of the present application has the characteristics of abundant raw material resources, low price, simple and efficient preparation process, etc. This method can realize the large-scale preparation of high-performance coal-based hard carbon negative electrodes, promote the high-value utilization of coal resources, and create higher economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0031] Figure 1 Differential scanning calorimetry (DSC) curves of the high-oxidation-activity coal powder prepared in Example 1 and untreated coal powder in an air atmosphere.

[0032] Figure 2 Transmission electron microscope image of the coal-based hard carbon prepared in Example 1.

[0033] Figure 3Small angle X-ray scattering pattern of coal-based hard carbon prepared in Example 1 and untreated coal-based hard carbon.

[0034] Figure 4 Charge-discharge curve of coal-based hard carbon prepared in Example 1 and untreated coal-based hard carbon. DETAILED DESCRIPTION

[0035] For a more complete understanding of the present application, it will be described in detail with reference to the following description. However, the present application is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the overall understanding of the disclosure of the present application.

[0036] Example 1

[0037] Step 1, 10 g of bituminous coal was pulverized in a pulverizer and sieved through a 200 mesh sieve to obtain coal powder with a particle size of ≤ 74 μm; then the coal powder was placed in a beaker, 25 mL of 2 mol / L hydrochloric acid solution was added, and the mixture was heated and stirred in a 60°C water bath for 12 h. After filtration, the metal salt ash in the coal was removed; 25 mL of 20% hydrofluoric acid solution was added, and the mixture was heated and stirred in a 60°C water bath for 12 h. After filtration, the silicate ash in the coal was removed. Then, the coal powder was washed with deionized water until neutral, and dried to obtain ultra-pure coal powder.

[0038] Step 2, the ultra-pure coal powder was placed in a beaker, 300 mL of 1-methyl-2-pyrrolidone solution was taken, and the mixture was heated and stirred in an 80°C water bath for 6 h; the mixture was transferred to a centrifuge tube and centrifuged at a speed of 8000 rad / min for 10 min; the bottom precipitate was taken, washed with water, and dried after filtration.

[0039] Step 3, the dried coal powder and catechol were placed in a muffle furnace, heated to 100°C at a rate of 1°C / min under an argon atmosphere, and kept at 100°C for 2 h. Then, the mixture was cooled to room temperature to obtain coal powder with high oxidation reaction activity.

[0040] Step 4, the coal powder with high oxidation reaction activity was placed in a muffle furnace, heated to 330°C at a rate of 1°C / min under an air atmosphere, and kept at 330°C for 2 h. Then, the mixture was cooled to room temperature to obtain oxygen-enriched coal powder.

[0041] Step 5, the oxygen-enriched coal powder was placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under an argon atmosphere, and kept at 1300°C for 2 h to obtain coal-based hard carbon.

[0042] The oxygen content of the oxygen-enriched coal powder prepared in Example 1 was 29 wt.%, the closed pore average pore diameter of the coal-based hard carbon was 1.2 nm, the average pore wall thickness was 3 layers of carbon sheet, the pore wall carbon layer curvature was 0.28, and the interlayer spacing was 0.38 nm. The prepared coal-based hard carbon powder was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, the slurry was uniformly scraped on a current collector copper foil, and the electrode sheet was cut after drying. The battery was assembled in an argon atmosphere glove box, metal sodium was used as the counter electrode, and 1M NaPF6 (diethylene glycol dimethyl ether) solution was used as the electrolyte to assemble a CR2032 button cell. Test results show that the hard carbon anode has a reversible specific capacity of 329 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 86%.

[0043] Figure 1 Differential scanning calorimetry (DSC) curves of the high-oxidative-activity coal powder prepared in Example 1 and untreated coal powder in air atmosphere. It can be seen that both samples show an exothermic peak at 330°C, which corresponds to the formation of oxygen-containing functional groups. However, the peak at this position of the high-oxidative-activity coal powder prepared in Example 1 is more sharp, indicating that it forms more abundant oxygen-containing functional groups. Figure 1

[0044] Figure 2 Transmission electron microscope image of the coal-based hard carbon prepared in Example 1. It can be seen that due to the introduction of abundant three-dimensional cross-linked structure by the high-oxidative-activity coal powder, the curved carbon sheet crystallites in the coal-based hard carbon prepared in Example 1 are arranged in disorder and surround each other to form abundant nano-pore structure. Figure 2

[0045] Figure 3 Small-angle X-ray scattering graph of the coal-based hard carbon prepared in Example 1 and untreated coal-based hard carbon. It can be seen that the scattering vector (Q) of the coal-based hard carbon prepared in Example 1 appears a clear hump at about 0.1 Å, which indicates that the obtained coal-based hard carbon has abundant highly connected nano-pore structure inside. Figure 3

[0046] Figure 4 Charge-discharge curve of the coal-based hard carbon prepared in Example 1 and untreated coal-based hard carbon. It can be seen that the coal-based hard carbon prepared in Example 1 exhibits high reversible specific capacity as a negative electrode material of sodium ion battery. At a current density of 20 mA / g, the reversible capacity of the sample is 329 mAh / g, and the first coulombic efficiency is 86%. In comparison, the reversible capacity of the untreated coal-based hard carbon is only 278 mAh / g, and the first coulombic efficiency is 85.

[0047] Example 2

[0048] ​​​The difference between this example and Example 1 is that: when assembling the CR2025 button cell, the counter electrode used is lithium metal, and the electrolyte is a 1M LiPF6 (diethylene glycol dimethyl ether) solution. Other steps and parameters are the same as in Example 1.

[0049] The oxygen-enriched coal powder prepared in Example 2 has an oxygen content of 29 wt.%, the closed pore average pore diameter of the coal-based hard carbon is 1.2 nm, the average pore wall thickness is 3 layers of carbon sheet layers, the pore wall carbon layer curvature is 0.28, and the interlayer spacing is 0.38 nm. The prepared coal-based hard carbon powder is mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, the slurry is uniformly scraped onto a current collector copper foil, and the dried electrode sheet is cut. The battery is assembled in an argon atmosphere glove box, metal lithium is used as the counter electrode, 1M LiPF6 (diethylene glycol dimethyl ether) solution is used as the electrolyte, and a CR2025 button cell is assembled. Test results show that the hard carbon negative electrode has a reversible specific capacity of 405 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 87%.

[0050] Example 3

[0051] The difference between this example and Example 1 is that: the raw coal used in step 1 is lignite, and the oxidation condition in step 4 is liquid phase oxidation. Other steps and parameters are the same as in Example 1.

[0052] The specific operation of step 4 liquid phase oxidation is as follows: the coal powder with high oxidation reaction activity is mixed with hydrogen peroxide at a mass ratio of 1:1, and is uniformly mixed at a temperature of 50°C for 12 hours. After filtration, washing and drying, an oxygen-enriched coal powder is obtained.

[0053] The oxygen-enriched coal powder prepared in Example 3 has an oxygen content of 21 wt.%, the closed pore average pore diameter of the coal-based hard carbon is 1.9 nm, the average pore wall thickness is 3 layers of carbon sheet layers, the pore wall carbon layer curvature is 0.21, and the interlayer spacing is 0.37 nm. The prepared coal-based hard carbon powder is mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, the slurry is uniformly scraped onto a current collector copper foil, and the dried electrode sheet is cut. The battery is assembled in an argon atmosphere glove box, metal sodium is used as the counter electrode, 1M NaPF6 (diethylene glycol dimethyl ether) solution is used as the electrolyte, and a CR2032 button cell is assembled. Test results show that the hard carbon negative electrode has a reversible specific capacity of 332 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 85%.

[0054] Example 4

[0055] The difference between this example and Example 1 is that: the organic solvent used in step 2 is tetrahydrofuran, and the hydrothermal temperature is 60°C. Other steps and parameters are the same as in Example 1.

[0056] The oxygen content of the oxygen-enriched coal powder prepared in Example 4 is 27 wt.%, the average pore size of the coal-based hard carbon is 1.6 nm, the average pore wall thickness is 4 layers of carbon sheets, the pore wall carbon layer curvature is 0.25, and the interlayer spacing is 0.38 nm. The prepared coal-based hard carbon powder is mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, the slurry is uniformly scraped on a current collector copper foil, and the electrode sheet is cut after drying. The battery is assembled in an argon atmosphere glove box, metal sodium is used as the counter electrode, and 1M NaPF6 (diethylene glycol dimethyl ether) solution is used as the electrolyte to assemble a CR2032 button cell. Test results show that the hard carbon anode has a reversible specific capacity of 312 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 88%.

[0057] Example 5

[0058] The difference between this example and Example 1 is that the hydrogen donor reagent used in step 3 is hydroquinone. Other steps and parameters are the same as those in Example 1.

[0059] The oxygen content of the oxygen-enriched coal powder prepared in Example 5 is 29 wt.%, the average pore size of the coal-based hard carbon is 1.2 nm, the average pore wall thickness is 3 layers of carbon sheets, the pore wall carbon layer curvature is 0.28, and the interlayer spacing is 0.38 nm. The prepared coal-based hard carbon powder is mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, the slurry is uniformly scraped on a current collector copper foil, and the electrode sheet is cut after drying. The battery is assembled in an argon atmosphere glove box, metal sodium is used as the counter electrode, and 1M NaPF6 (diethylene glycol dimethyl ether) solution is used as the electrolyte to assemble a CR2032 button cell. Test results show that the hard carbon anode has a reversible specific capacity of 325 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 85%.

[0060] Example 6

[0061] The difference between this example and Example 1 is that the oxidation condition in step 4 is solid phase oxidation. Other steps and parameters are the same as those in Example 1.

[0062] The specific operation of the solid phase oxidation in step 4 is as follows: the coal powder with high oxidation reactivity is mixed with manganese dioxide at a mass ratio of 1:1, and is uniformly mixed at a temperature of 400°C for 2 h, and is filtered, washed with water and dried to obtain an oxygen-enriched coal powder.

[0063] The oxygen content of the oxygen-enriched coal powder prepared in Example 6 was 25 wt.%, the average pore size of the coal-based hard carbon was 1.7 nm, the average pore wall thickness was 3 layers of carbon sheets, the pore wall carbon layer curvature was 0.28, and the interlayer spacing was 0.38 nm. The prepared coal-based hard carbon powder was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, the slurry was uniformly scraped on a current collector copper foil, and the electrode sheet was cut after drying. The battery was assembled in an argon atmosphere glove box, metal sodium was used as the counter electrode, 1M NaPF6 (diethylene glycol dimethyl ether) solution was used as the electrolyte, and a CR2032 button cell was assembled. Test results show that the hard carbon anode has a reversible specific capacity of 330 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 85%.

[0064] Example 7

[0065] The difference between this example and Example 1 is that in step 2, 500 mL of 1-methyl-2-pyrrolidone solution was placed in a 120°C oil bath and heated and stirred for 12 h.

[0066] The oxygen content of the oxygen-enriched coal powder prepared in Example 7 was 23 wt.%, the average pore size of the coal-based hard carbon was 1.8 nm, the average pore wall thickness was 2 layers of carbon sheets, the pore wall carbon layer curvature was 0.25, and the interlayer spacing was 0.38 nm. The prepared coal-based hard carbon powder was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, the slurry was uniformly scraped on a current collector copper foil, and the electrode sheet was cut after drying. The battery was assembled in an argon atmosphere glove box, metal sodium was used as the counter electrode, 1M NaPF6 (diethylene glycol dimethyl ether) solution was used as the electrolyte, and a CR2032 button cell was assembled. Test results show that the hard carbon anode has a reversible specific capacity of 335 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 88%.

[0067] Example 8

[0068] The difference between this example and Example 1 is that the gas phase oxidation conditions in step 4 are as follows: the oxidation atmosphere is oxygen, the gas flow rate is 300 m³ / h, the muffle furnace temperature is 300°C, and the holding time is 5 h. The other steps and parameters are the same as in Example 1.

[0069] The oxygen content of the oxygen-enriched coal powder prepared in Example 8 is 30 wt.%, the closed pore average pore size of the coal-based hard carbon is 1.7 nm, the average pore wall thickness is 2 layers of carbon sheet layers, the pore wall carbon layer curvature is 0.29, and the interlayer spacing is 0.38 nm. The prepared coal-based hard carbon powder is mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, and the slurry is uniformly coated on a current collector copper foil. After drying, the electrode sheet is cut. The battery is assembled in an argon atmosphere glove box, metal sodium is used as the counter electrode, and 1M NaPF6 (diethylene glycol dimethyl ether) solution is used as the electrolyte to assemble a CR2032 button cell. Test results show that the hard carbon anode has a reversible specific capacity of 340 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 87%.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that Comparative Example 1 does not use an organic solvent in step 3. The other steps and parameters of Comparative Example 1 are the same as those of Example 1.

[0072] The coal-based hard carbon prepared in Comparative Example 1 is mixed with carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, and then the slurry is uniformly coated on a current collector copper foil. After drying, the electrode sheet is cut. The battery is assembled in an argon atmosphere glove box, metal sodium is used as the counter electrode, and 1M NaPF6 (diethylene glycol dimethyl ether) solution is used as the electrolyte to assemble a CR2032 button cell. Test results show that the hard carbon anode has a reversible specific capacity of 289 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 78%.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 1 is that Comparative Example 1 does not use a hydrogen donor reagent in step 3. The other steps and parameters of Comparative Example 2 are the same as those of Example 1.

[0075] The coal-based carbon material prepared in Comparative Example 2 is mixed with carbon black and polyvinylidene fluoride at a mass ratio of 80:10:10 to form a slurry, and then the slurry is uniformly coated on a current collector copper foil. After drying, the electrode sheet is cut. The battery is assembled in an argon atmosphere glove box, metal sodium is used as the counter electrode, and 1M NaPF6 (diethylene glycol dimethyl ether) solution is used as the electrolyte to assemble a CR2032 button cell. Test results show that the hard carbon anode has a reversible specific capacity of 256 mAh / g at a current density of 20 mA / g, and a first coulombic efficiency of 71%.

[0076] The details of the application not described herein are considered known to those skilled in the art. Although the foregoing description of the application has been described in some detail for the purposes of clarity and the understanding of the application, it should be appreciated that the application is not limited to the particular embodiments or examples described. It should be readily understood that various changes can be made therein without departing from the spirit and scope of the application defined by the appended claims and that equivalent materials can be substituted for those described.

Claims

1. A method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal, characterized in that: The following steps are involved: Step 1: crushing and deashing the raw coal to obtain ultra-pure coal powder; Step 2: uniformly mixing the ultrapure coal powder with an oxygen-containing organic solvent, stirring under heat preservation to dissolve and remove chemically inert components in the coal, centrifuging and collecting the precipitate, washing with water, and drying to obtain the treated coal powder; Step 3: heat-treating the treated coal powder with a hydrogen-donating organic reagent, using hydrogen radicals released by the hydrogen-donating reagent to attack and destroy the strongly conjugated aromatic ring structure in the coal molecules, and then cooling to room temperature to obtain coal powder with high oxidation reaction activity; Step 4, oxidatively cross-linking the high oxidation reaction active coal powder through a pre-oxidation method to obtain oxygen-enriched coal powder; In step 5, the oxygen-enriched pulverized coal is carbonized at high temperature under the protection of an inert gas to obtain an amorphous carbon material with a highly disordered microcrystalline structure, namely, coal-based hard carbon.

2. The method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal according to claim 1, characterized in that: In step 1, the deashing is performed by washing with acid solutions of different types and concentrations, wherein the acid solution includes one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid or nitric acid, with a concentration of 0.1-10 mol / L; the particle size of the ultra-pure coal powder after deashing is ≤100 μm, and the ash content is 0.1-1.0 wt.%.

3. The method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal according to claim 1, characterized in that: The oxygen-containing organic solvent is one or more of 1-methyl-2-pyrrolidone, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran, ether, and isopropanol, and the coal-dissolving ratio of the oxygen-containing organic solvent to the ultra-pure coal powder is 5:1 to 50:

1.

4. The method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal according to claim 1, characterized in that: The hydrogen-donating organic reagent includes one or more of o-diphenol, p-diphenol, sorbitol, butyl-tert-catechol, glycine, and sodium glutamate.

5. The method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal according to claim 1, characterized in that: The temperature of the heat preservation and stirring in step 2 is 30-120°C, and the heat preservation time is 0.5-24 hours; The temperature of the heat preservation treatment in step 3 is 30-200° C., and the heat preservation time is 0.5-24 h.

6. The method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal according to claim 1, characterized in that: In step 4, the high oxidation reaction active coal powder is oxidatively cross-linked by a pre-oxidation method to obtain oxygen-enriched coal powder. Specifically, the following steps are performed: The pre-oxidation method is gas phase pre-oxidation, liquid phase pre-oxidation or solid phase pre-oxidation; The gas phase pre-oxidation conditions are as follows: the oxidizing atmosphere for the heat preservation pre-oxidation includes oxygen or air, the gas flow rate is 50-500 m³ / h, the muffle furnace temperature is 100-500°C, and the heat preservation time is 0.5-24 h; The liquid phase pre-oxidation conditions are as follows: the oxidant is one or more of hydrogen peroxide, sodium hypochlorite, ammonium persulfide, and sulfuric acid, the mass ratio of the oxidant to the coal is 0.5:1 to 5:1, the reaction temperature is 30 to 80°C, and the reaction time is 4 to 24 hours; The solid phase pre-oxidation conditions are as follows: the oxidant is one or more of manganese dioxide, potassium permanganate, sodium nitrite, and potassium dichromate, the mass ratio of the oxidant to coal is 0.1:1~2:1, the reaction temperature is 80~300°C, and the reaction time is 0.5~5h.

7. The method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal according to claim 1, characterized in that: In step 5, the high-temperature carbonization is carried out under the protection of an inert gas, specifically: the inert gas is one of argon and nitrogen.

8. The method for preparing coal-based hard carbon by enhancing the oxidation reaction activity of coal according to claim 1, characterized in that: The temperature of the high-temperature carbonization in step 5 is 800-1500° C., the heating rate is 0.5-10° C. / min, and the holding time is 0.5-6 h.

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 oxygen content of the oxygen-enriched coal powder is 25-40 wt.%, the average closed pore diameter of the coal-based hard carbon is 0.3-2 nm, the average pore wall thickness is 0.3-1 nm, the pore spacing is 2-8 nm, the pore wall carbon layer curvature is 0.2-0.4, and the interlayer spacing is 0.37-0.40 nm.

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 sodium ion batteries, lithium ion batteries or potassium ion batteries.

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