Coal-based hard carbon negative electrode material with high slope lithium storage capacity as well as preparation method and application of coal-based hard carbon negative electrode material

Abstract

The invention belongs to the technical field of hybrid supercapacitors, and discloses a coal-based hard carbon negative electrode material with high slope lithium storage capacity and a preparation method and application of the coal-based hard carbon negative electrode material. Washing the pulverized coal subjected to impurity removal with ultrapure water until the pH value is neutral, and then drying; pre-oxidizing the pulverized coal in an air atmosphere at 280-320 DEG C for 110-130 minutes, switching a gas atmosphere into a protective atmosphere after the pre-oxidation is finished, continuously heating, carbonizing at 1180-1220 DEG C for 110-130 minutes, washing with an acid solution to be neutral after the carbonization is finished, and drying to obtain a carbon material subjected to heat treatment; impregnating the surface of the carbon material subjected to heat treatment with lithium fluoride; and carrying out heat treatment on the material A at 280-320 DEG C in a protective atmosphere for 280-320 minutes to obtain the coal-based hard carbon negative electrode material with high slope lithium storage capacity. The power and capacity performance of the hybrid super capacitor can be improved, the intrinsic safety of the device can be further improved, and the hybrid super capacitor has great practical significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of hybrid supercapacitors, and in particular relates to a coal-based hard carbon negative electrode material with high slope lithium storage capacity, and a preparation method and application thereof. Background Art

[0002] As a new type of energy storage device, hybrid supercapacitors combine the advantages of lithium-ion batteries and supercapacitors, with high energy density, long cycle life and good safety. They have the potential to replace lithium-ion batteries and flywheel energy storage in the field of power frequency modulation. However, most of the lithium storage hard carbon materials used in the negative electrode of hybrid supercapacitors are imported products, and their structures are often designed for lithium batteries, which results in the slope area capacity of only 150mAh / g in their capacity distribution; if they are applied to hybrid supercapacitors, it will lead to insufficient available capacity and large amount of electrode materials, which will further cause cost waste; and in the case of overcharging, the negative electrode charge may penetrate into the platform area, generating lithium dendrites and causing safety risks. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a coal-based hard carbon negative electrode material with a high slope lithium storage capacity and a preparation method and application thereof. The present invention not only helps to improve the power and capacity performance of hybrid supercapacitors, but also can further improve the intrinsic safety of the device, and has great practical significance.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for preparing a coal-based hard carbon negative electrode material with high slope lithium storage capacity comprises the following steps: The pulverized coal is cleaned with an alkaline solution to obtain cleaned pulverized coal; The impurity-removed coal powder is washed with ultrapure water until the pH value is neutral, and then dried to obtain pretreated coal powder; The pretreated pulverized coal is pre-oxidized in an air atmosphere at 280-320°C for 110-130 minutes, and after the pre-oxidation, the gas atmosphere is switched to a protective atmosphere, and the temperature is continued to be raised, and carbonized at 1180-1220°C for 110-130 minutes. After the carbonization, it is washed with acid solution until neutral and dried to obtain a heat-treated carbon material; The surface of the heat-treated carbon material is impregnated with lithium fluoride to obtain material A; The material A is heat treated at 280-320° C. for 280-320 minutes in a protective atmosphere to obtain the coal-based hard carbon negative electrode material with a high slope lithium storage capacity.

[0005] Preferably, the coal powder is at least one of lignite and sub-bituminous coal.

[0006] Preferably, the mesh size of the coal powder is above 100 meshes.

[0007] Preferably, when the coal powder is removed from the coal by using an alkaline solution, the following process is included: The coal powder is placed in an alkaline solution and magnetically stirred at 78-82°C for 280-320 minutes, followed by solid-liquid separation and drying to obtain the impurity-removed coal powder.

[0008] Preferably, the alkaline solution is a 4.8-5.2M NaOH solution, and the ratio of coal powder to NaOH solution is: 1-3g coal powder is added to every 25ml NaOH solution.

[0009] Preferably, after carbonization, when washing with acid solution until neutral, 0.8-1.2M dilute hydrochloric acid is used for washing.

[0010] Preferably, the process of impregnating the surface of the heat-treated carbon material with lithium fluoride to obtain material A comprises: The heat-treated carbon material is added to a lithium fluoride monohydrate solution, and ultrasonically mixed for 10 to 80 minutes, followed by vacuum impregnation and drying to obtain the material A.

[0011] Preferably, in the lithium fluoride monohydrate solution, the mass content of lithium fluoride is 2%~4%; the mass ratio of the heat-treated carbon material to lithium fluoride is (0.5~2):1.

[0012] The present invention also provides a coal-based hard carbon negative electrode material with a high slope lithium storage capacity, and the coal-based hard carbon negative electrode material with a high slope lithium storage capacity is prepared by the above-mentioned preparation method of the present invention.

[0013] The present invention also provides an application of the coal-based hard carbon negative electrode material with high slope lithium storage capacity as described above, wherein the coal-based hard carbon negative electrode material with high slope lithium storage capacity is used as a lithium storage hard carbon material for a capacitor negative electrode.

[0014] The present invention has the following beneficial effects: In the preparation method of the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention, the coal powder is decontaminated with an alkaline solution, which can effectively remove impurity elements such as Al and Si in the coal powder to prevent these impurity elements from affecting the performance in the battery. After decontamination, the coal powder is purer, which can improve conductivity or reduce side reactions. The purpose of washing the decontaminated coal powder with ultrapure water to a neutral pH value is to remove the alkaline solution used in the decontamination process and avoid unnecessary reactions during subsequent treatments. The pretreated coal powder is pre-oxidized in an air atmosphere, which can destroy the ordered aromatic ring structure in the coal, which is conducive to the generation of short-range ordered and long-range disordered hard carbon structures. Coal, as a precursor, has a higher carbon yield than synthetic resins and biomass, which is conducive to reducing the preparation cost of materials. Then, high-temperature carbonization under a protective atmosphere is beneficial to enhance the conductivity and maintain the disordered structure of hard carbon. The high slope capacity of the coal-based hard carbon negative electrode material of the present invention comes from the unique pore structure and defects formed by the pre-oxidation of coal powder and the imprinting effect of lithium fluoride. These structures provide more lithium storage sites, especially the adsorption storage capacity of lithium corresponding to the slope area. After the carbonization is completed, it is washed with acid solution to neutrality, which can remove impurities and residual metals generated during the carbonization process, further purify the material, and ensure electrochemical stability. The surface of the heat-treated carbon material is impregnated with lithium fluoride, and heat-treated at 280-320°C in a protective atmosphere. Lithium fluoride can induce the generation of doping defects, improve the reversible capacity of the hard carbon slope, and can also form a LiF layer on the surface of the carbon material, which helps to stabilize the solid electrolyte interface (SEI) film, reduce electrolyte decomposition and electrode pulverization, and improve the cycle life; in addition, the introduction of lithium fluoride can improve the interface performance of the material, promote the diffusion of lithium ions, help to improve the power and capacity performance of the hybrid supercapacitor, and further improve the intrinsic safety of the device, which has great practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a microscopic morphology of the coal-based hard carbon negative electrode material with high slope lithium storage capacity prepared in Example 1 of the present invention; Figure 2 This is a graph showing the specific capacity of the coal-based hard carbon negative electrode material with high slope lithium storage capacity prepared in an embodiment of the present invention and the hard carbon material not modified with lithium salt. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention comprises the following steps: Step 1. Use coal as raw material, grind the coal into powder and sieve it with 100-200 mesh to obtain coal powder; the coal should have the following characteristics: low ash and high alkali. The purpose of low ash is to control the residual ash in the product hard carbon; the purpose of high alkali is to make the graphitization degree of the product hard carbon higher, which can improve the conductivity; lignite and sub-bituminous coal have low metamorphism and high volatile matter, which can form a pore structure that is conducive to slope lithium storage. Therefore, the coal used in the present invention is a mixture of one or two of lignite and sub-bituminous coal.

[0018] Step 2. Place the coal powder in a 4.8-5.2M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 280-320 minutes, wherein the ratio of coal powder to NaOH solution is 1-3g / 25ml, so as to remove elements such as Al and Si in the coal.

[0019] Step 3. Wash the coal powder obtained in step 2 with ultrapure water for multiple times until the pH value is neutral, and then dry it for later use.

[0020] Step 4. Pre-oxidize the pulverized coal obtained in step 3 at 280-320 degrees Celsius in an air atmosphere for 100-140 minutes; then switch the gas source to argon, continue to heat to 1180-1220 degrees Celsius for carbonization for 100-140 minutes, and obtain a carbon material. Wash the obtained carbon material with 0.8-1.2M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0021] Step 5. Add the carbon material obtained in step 4 to an ultrapure aqueous solution of lithium fluoride monohydrate, wherein the mass percentage of lithium fluoride in the lithium fluoride monohydrate solution is 2% to 4%, and the mass ratio of the heat-treated carbon material to lithium fluoride is (0.5 to 2):1. After ultrasonic mixing for 40 to 80 minutes, vacuum impregnation and drying are performed.

[0022] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 280-320 degrees Celsius for 280-320 minutes to obtain the final product (i.e., the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention).

[0023] Example 1 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Using lignite as raw material, grinding the lignite and sieving it with 200 mesh to obtain coal powder; Step 2. Place the coal powder in a 5.0M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 300 minutes, wherein the ratio of coal powder to NaOH solution is 2g / 25ml.

[0024] Step 3. Wash the coal powder obtained in step 2 with ultrapure water five times until the pH value is neutral, and then dry it for later use.

[0025] Step 4. Pre-oxidize the coal powder obtained in step 3 at 300 degrees Celsius in air atmosphere for 120 minutes; then switch the gas source to argon, continue to heat to 1200 degrees Celsius for carbonization for 120 minutes, and obtain a carbon material. Wash the obtained carbon material with 1.0M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0026] Step 5. Add the carbon material obtained in step 4 to an ultrapure aqueous solution of lithium fluoride monohydrate, wherein the mass percentage of lithium fluoride in the lithium fluoride monohydrate solution is 3%, and the mass ratio of the heat-treated carbon material to lithium fluoride is 1:1. After ultrasonic mixing for 60 minutes, vacuum impregnation and drying are performed.

[0027] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 300 degrees Celsius for 300 minutes to obtain a final product.

[0028] See also Figure 1 It can be seen that there are growing lithium fluoride crystals on the surface of the carbon material. During the battery cycle, these crystals will participate in the formation process of SEI and effectively improve the initial efficiency.

[0029] The carbon material obtained in this embodiment was tested by a button half-cell, and the first-cycle coulombic efficiency could reach 73%, and the reversible slope capacity could reach 240 mAh / g.

[0030] Comparative Example 1 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Using lignite as raw material, grinding the lignite and sieving it with 200 mesh to obtain coal powder; Step 2. Place the coal powder in a 5.0M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 300 minutes, wherein the ratio of coal powder to NaOH solution is 2g / 25ml.

[0031] Step 3. Wash the coal powder obtained in step 2 with ultrapure water five times until the pH value is neutral, and then dry it for later use.

[0032] Step 4. Pre-oxidize the coal powder obtained in step 3 at 300 degrees Celsius in air atmosphere for 120 minutes; then switch the gas source to argon, continue to heat to 1200 degrees Celsius for carbonization for 120 minutes, and obtain a carbon material. Wash the obtained carbon material with 1.0M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0033] Step 5. The carbon material obtained in step 4 is heat treated in a tubular furnace in an argon atmosphere at 300 degrees Celsius for 300 minutes to obtain a final product.

[0034] The carbon material obtained in this comparative example was tested by a button half-cell, and the first-cycle coulombic efficiency was about 64%, and the reversible slope capacity was about 206 mAh / g.

[0035] See also Figure 2 , the comparative example product is unmodified hard carbon. Although the first-cycle slope discharge capacity can reach 325mAh / g, the charging capacity is only 206mAh / g, and the first-cycle coulombic efficiency is 64%; and the lithium salt-modified hard carbon obtained based on Example 1 has a first-cycle slope discharge capacity of 300mAh / g, a charging capacity of 240mAh / g, a first-cycle coulombic efficiency of 80%, and a greatly improved reversible capacity. In order to construct a hard carbon material with a high slope lithium storage capacity, it is necessary to increase the concentration of surface lithium storage sites, but the surface lithium storage sites will also cause thicker SEI to form and reduce the first-cycle coulombic efficiency. The present invention directly participates in the SEI generation through lithium fluoride modification, thereby achieving an increase in the first efficiency and reversible slope capacity.

[0036] Example 2 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Using lignite as raw material, grinding the coal into powder and then sieving it with 200 mesh to obtain coal powder; Step 2. Place the coal powder in a 5.0M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 300 minutes, wherein the ratio of coal powder to NaOH solution is 2g / 25ml.

[0037] Step 3. Wash the coal powder obtained in step 2 with ultrapure water until the pH value is neutral, and then dry it for later use.

[0038] Step 4. Pre-oxidize the coal powder obtained in step 3 at 280 degrees Celsius in an air atmosphere for 100 minutes; then switch the gas source to argon, continue to heat to 1180 degrees Celsius for carbonization for 140 minutes, and obtain a carbon material. Wash the obtained carbon material with 1.0M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0039] Step 5. Add the carbon material obtained in step 4 to an ultrapure aqueous solution of lithium fluoride monohydrate (lithium fluoride), wherein the mass percentage of lithium fluoride in the lithium fluoride monohydrate solution is 4%, and the mass ratio of the heat-treated carbon material to lithium fluoride is 0.5:1. After ultrasonic mixing for 70 minutes, vacuum impregnation and drying are performed.

[0040] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 290 degrees Celsius for 310 minutes to obtain the final product (i.e., the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention).

[0041] The carbon material obtained in this embodiment was tested by a button half-cell, and the first-cycle coulombic efficiency could reach 76%, and the reversible slope capacity could reach 210 mAh / g.

[0042] Example 3 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Using lignite as raw material, grinding the coal into powder and then sieving it with 200 mesh to obtain coal powder; Step 2. Place the coal powder in a 4.8M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 320 minutes, wherein the ratio of coal powder to NaOH solution is 1 g / 25 ml.

[0043] Step 3. Wash the coal powder obtained in step 2 with ultrapure water until the pH value is neutral, and then dry it for later use.

[0044] Step 4. Pre-oxidize the coal powder obtained in step 3 at 320 degrees Celsius in air atmosphere for 140 minutes; then switch the gas source to argon, continue to heat to 1180 degrees Celsius for carbonization for 140 minutes, and obtain a carbon material. Wash the obtained carbon material with 1.2M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0045] Step 5. The carbon material obtained in step 4 is added to an ultrapure aqueous solution of lithium fluoride monohydrate (in the lithium fluoride monohydrate solution, the mass percentage of lithium fluoride is 4%, the mass ratio of the heat-treated carbon material to lithium fluoride is 1:2, and the mixture is ultrasonically mixed for 80 minutes and then vacuum impregnated and dried.

[0046] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 280 degrees Celsius for 320 minutes to obtain the final product (i.e., the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention).

[0047] The carbon material obtained in this embodiment was tested by a button half-cell, and the first-cycle coulombic efficiency could reach 77%, and the reversible slope capacity could reach 210 mAh / g.

[0048] Example 4 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Use subbituminous coal as raw material, grind the coal into powder and then sieve it with 100 mesh to obtain coal powder; Step 2. Place the coal powder in a 4.8M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 320 minutes, wherein the ratio of coal powder to NaOH solution is 3g / 25ml.

[0049] Step 3. Wash the coal powder obtained in step 2 with ultrapure water until the pH value is neutral, and then dry it for later use.

[0050] Step 4. Pre-oxidize the coal powder obtained in step 3 at 300 degrees Celsius in air atmosphere for 140 minutes; then switch the gas source to argon, continue to heat to 1200 degrees Celsius for carbonization for 120 minutes, and obtain a carbon material. Wash the obtained carbon material with 0.8M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0051] Step 5. The carbon material obtained in step 4 is added to an ultrapure aqueous solution of lithium fluoride monohydrate (, in the lithium fluoride monohydrate solution, the mass percentage of lithium fluoride is 3%, the mass ratio of the heat-treated carbon material to lithium fluoride is 1:2, and the mixture is ultrasonically mixed for 60 minutes and then vacuum impregnated and dried.

[0052] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 310 degrees Celsius for 310 minutes to obtain the final product (i.e., the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention).

[0053] The carbon material obtained in this embodiment was tested by a button half-cell, and the first-cycle coulombic efficiency could reach 80%, and the reversible slope capacity could reach 230 mAh / g.

[0054] Example 5 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Use subbituminous coal as raw material, grind the coal into powder and then sieve it with 100 mesh to obtain coal powder; Step 2. Place the coal powder in a 5.2M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 280 minutes, wherein the ratio of coal powder to NaOH solution is 2g / 25ml.

[0055] Step 3. Wash the coal powder obtained in step 2 with ultrapure water until the pH value is neutral, and then dry it for later use.

[0056] Step 4. Pre-oxidize the coal powder obtained in step 3 at 280 degrees Celsius in an air atmosphere for 120 minutes; then switch the gas source to argon, continue to heat to 1220 degrees Celsius for carbonization for 120 minutes, and obtain a carbon material. Wash the obtained carbon material with 0.8M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0057] Step 5. The carbon material obtained in step 4 is added to an ultrapure aqueous solution of lithium fluoride monohydrate (, in the lithium fluoride monohydrate solution, the mass percentage of lithium fluoride is 4%, the mass ratio of the heat-treated carbon material to lithium fluoride is 1:1, and the mixture is ultrasonically mixed for 80 minutes and then vacuum impregnated and dried.

[0058] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 320 degrees Celsius for 300 minutes to obtain the final product (i.e., the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention).

[0059] The carbon material obtained in this embodiment was tested by a button half-cell, and the first-cycle coulombic efficiency could reach 80%, and the reversible slope capacity could reach 220 mAh / g.

[0060] Example 6 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Use subbituminous coal as raw material, grind the coal into powder and then sieve it with 150 mesh to obtain coal powder; Step 2. Place the coal powder in a 5.2M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 280 minutes, wherein the ratio of coal powder to NaOH solution is 1 g / 25 ml.

[0061] Step 3. Wash the coal powder obtained in step 2 with ultrapure water until the pH value is neutral, and then dry it for later use.

[0062] Step 4. Pre-oxidize the coal powder obtained in step 3 at 280 degrees Celsius in an air atmosphere for 100 minutes; then switch the gas source to argon, continue to heat to 1220 degrees Celsius for carbonization for 100 minutes, and obtain a carbon material. Wash the obtained carbon material with 0.8M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0063] Step 5. Add the carbon material obtained in step 4 to an ultrapure aqueous solution of lithium fluoride monohydrate, wherein the mass percentage of lithium fluoride in the lithium fluoride monohydrate solution is 4%, and the mass ratio of the heat-treated carbon material to lithium fluoride is 1:1.5. After ultrasonic mixing for 70 minutes, vacuum impregnation and drying are performed.

[0064] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 315 degrees Celsius for 290 minutes to obtain the final product (i.e., the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention).

[0065] The carbon material obtained in this embodiment was tested by a button half-cell, and the first-cycle coulombic efficiency could reach 80%, and the reversible slope capacity could reach 210 mAh / g.

[0066] Example 7 The method for preparing the coal-based hard carbon negative electrode material with high slope lithium storage capacity in this embodiment comprises the following steps: Step 1. Using sub-bituminous coal and lignite (mass ratio of 1:1) as raw materials, grinding the coal and then sieving it with 200 mesh to obtain coal powder; Step 2. Place the coal powder in a 5.0M NaOH solution and stir it magnetically at 80±2 degrees Celsius for 300 minutes, wherein the ratio of coal powder to NaOH solution is 3g / 25ml.

[0067] Step 3. Wash the coal powder obtained in step 2 with ultrapure water until the pH value is neutral, and then dry it for later use.

[0068] Step 4. Pre-oxidize the coal powder obtained in step 3 at 300 degrees Celsius in air atmosphere for 120 minutes; then switch the gas source to argon, continue to heat to 1200 degrees Celsius for carbonization for 120 minutes, and obtain a carbon material. Wash the obtained carbon material with 1.0M dilute hydrochloric acid for multiple times until the pH value is neutral, and dry it for later use.

[0069] Step 5. The carbon material obtained in step 4 is added to an ultrapure aqueous solution of lithium fluoride monohydrate (, in the lithium fluoride monohydrate solution, the mass percentage of lithium fluoride is 3%, the mass ratio of the heat-treated carbon material to lithium fluoride is 1:1.5, and then the mixture is ultrasonically mixed for 70 minutes and vacuum impregnated and dried.

[0070] Step 6. The carbon material obtained in step 5 is heat treated in a tubular furnace in an argon atmosphere at 300 degrees Celsius for 280 minutes to obtain the final product (i.e., the coal-based hard carbon negative electrode material with high slope lithium storage capacity of the present invention).

[0071] The carbon material obtained in this embodiment was tested by a button half-cell, and the first-cycle coulombic efficiency could reach 80%, and the reversible slope capacity could reach 230 mAh / g.

[0072] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a coal-based hard carbon negative electrode material with high slope lithium storage capacity, characterized in that: The process includes the following: The pulverized coal is cleaned with an alkaline solution to obtain cleaned pulverized coal; The impurity-removed coal powder is washed with ultrapure water until the pH value is neutral, and then dried to obtain pretreated coal powder; The pretreated pulverized coal is pre-oxidized in an air atmosphere at 280-320°C for 110-130 minutes, and after the pre-oxidation, the gas atmosphere is switched to a protective atmosphere, and the temperature is continued to be raised, and carbonized at 1180-1220°C for 110-130 minutes. After the carbonization, it is washed with acid solution until neutral and dried to obtain a heat-treated carbon material; The surface of the heat-treated carbon material is impregnated with lithium fluoride to obtain material A; The material A is heat treated at 280-320° C. for 280-320 minutes in a protective atmosphere to obtain the coal-based hard carbon negative electrode material with a high slope lithium storage capacity.

2. The method for preparing a coal-based hard carbon negative electrode material with a high slope lithium storage capacity according to claim 1, characterized in that: The coal powder is at least one of lignite and sub-bituminous coal.

3. The method for preparing a coal-based hard carbon negative electrode material with a high slope lithium storage capacity according to claim 1, characterized in that: The mesh number of the coal powder is above 100 meshes.

4. The method for preparing a coal-based hard carbon negative electrode material with a high slope lithium storage capacity according to claim 1, characterized in that: When coal powder is removed by alkaline solution, the following process is included: The coal powder is placed in an alkaline solution and magnetically stirred at 78-82°C for 280-320 minutes, followed by solid-liquid separation and drying to obtain the impurity-removed coal powder.

5. The method for preparing a coal-based hard carbon negative electrode material with a high slope lithium storage capacity according to claim 1 or 4, characterized in that: The alkaline solution uses 4.8~5.2M NaOH solution, and the usage ratio of coal powder to NaOH solution is: 1~3g coal powder is added to every 25ml NaOH solution.

6. The method for preparing a coal-based hard carbon negative electrode material with a high slope lithium storage capacity according to claim 1, characterized in that: After carbonization, use acid to wash until neutral, and use 0.8~1.2M dilute hydrochloric acid for washing.

7. The method for preparing a coal-based hard carbon negative electrode material with a high slope lithium storage capacity according to claim 1, characterized in that: The process of impregnating the surface of the heat-treated carbon material with lithium fluoride to obtain material A includes: The heat-treated carbon material is added to a lithium fluoride monohydrate solution, and ultrasonically mixed for 10 to 80 minutes, followed by vacuum impregnation and drying to obtain the material A.

8. The method for preparing a coal-based hard carbon negative electrode material with a high slope lithium storage capacity according to claim 1 or 7, characterized in that: The mass content of lithium fluoride in the lithium fluoride monohydrate solution is 2%~4%; the mass ratio of the carbon material after heat treatment to lithium fluoride is (0.5~2):

1.

9. A coal-based hard carbon negative electrode material with high slope lithium storage capacity, characterized in that: The coal-based hard carbon negative electrode material with high slope lithium storage capacity is prepared by any preparation method according to claims 1-8.

10. The use of the coal-based hard carbon negative electrode material with high slope lithium storage capacity according to claim 9, characterized in that: The coal-based hard carbon negative electrode material with high slope lithium storage capacity is used as a lithium storage hard carbon material for capacitor negative electrode.

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