A coal-based carbon negative electrode material for sodium ion batteries and its preparation method and application

Abstract

The present invention provides a coal-based carbon negative electrode material for sodium ion batteries, as well as a preparation method and application thereof. The provided method comprises: (1) soaking bituminous coal in a mixed acid solution containing hydrochloric acid and hydrofluoric acid, rinsing until the solution is neutral, and then drying to obtain dry coal powder; (2) mixing theabrownin with the dry coal powder, and then pre-oxidizing the mixture in an oxygen-containing atmosphere to obtain a pre-oxidized product; (3) carbonizing the pre-oxidized product in an inert atmosphere to obtain a coal-based carbon material. The coal-based carbon material can be used as a negative electrode for sodium ion batteries and has high capacity and first coulombic efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage hard carbon materials, and specifically relates to a coal-based carbon negative electrode material for sodium ion batteries, a preparation method and an application thereof. Background Art

[0002] The shortage of lithium resources has hampered the further development of lithium-ion batteries for large-scale energy storage. my country is rich in sodium resources, and sodium shares similar chemical properties with lithium, making sodium-ion batteries a promising alternative to lithium-ion batteries. Among sodium-ion battery anode materials, hard carbon holds the greatest commercial potential for sodium storage. Bituminous coal, with its abundant resources, low cost, and high carbon yield, is a highly promising anode material for sodium-ion batteries.

[0003] However, bituminous coal is a macromolecular structure of condensed aromatic hydrocarbons, which contains basic structural units composed of aromatic rings, fatty side chains and functional groups. During the pyrolysis process, the condensation of aromatic rings easily causes the growth of graphite crystals and increases the degree of graphitization, which is not conducive to the storage of sodium ions.

[0004] Chinese patent application CN114335522A describes the use of oxidizing agents, such as sulfur-containing reagents, to oxidize coal-based materials, followed by mixing with volatile organic compounds (VOCs), followed by low-temperature heat treatment, and finally high-temperature heat treatment to produce coal-based carbon anode materials. However, this design process introduces excessive oxygen through pre-oxidation with a strong oxidizing agent, resulting in a significant decrease in the carbonization yield of the coal. Furthermore, the process involves low-temperature pyrolysis and encapsulation of VOCs, which is time-consuming and unfavorable for large-scale development and application.

[0005] Chinese patent application publication number CN115784196A describes pre-treating coal in an oxygen-containing atmosphere, then pre-calcining the pre-treated coal and a co-treatment agent in a first stage, followed by a second stage of calcination under negative pressure, to produce a coal-based carbon anode material for sodium-ion batteries. This method is complex and uses co-treatment agents such as ammonium salts and transition metal salts, resulting in high costs.

[0006] Chinese patent application CN117105198A describes mixing coal and an inorganic salt, ball-milling the mixture in an oxygen-containing atmosphere, removing the inorganic salt from the mixture to obtain a coal-based precursor, and carbonizing the coal-based precursor to obtain the coal-based carbon material. This method also uses inorganic salts, which need to be removed, resulting in high costs and a complex process.

[0007] The preparation methods of coal-based carbon materials need to be further optimized. Summary of the Invention

[0008] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0009] In response to the above-mentioned technical deficiencies, the present invention provides a coal-based carbon negative electrode material for sodium ion batteries, as well as a preparation method and application. Theabrownin is a natural high-polymer complex extracted from Pu'er tea, and its surface is rich in functional groups such as carboxyl and hydroxyl groups. When bituminous coal and theabrownin are mixed, in an atmosphere of low-temperature oxygen, the oxygen-containing functional groups on the coal surface and the oxygen-containing functional groups of theabrownin undergo heterogeneous cross-linking. This cross-linking structure can hinder the growth of graphite crystallites during the subsequent pyrolysis process, forming a coal-based carbon amorphous structure that is conducive to the storage of sodium ions. The provided coal-based carbon material can be used to prepare the negative electrode of a sodium ion battery with high capacity and first coulombic efficiency.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] A first aspect of the present invention provides a method for preparing a coal-based carbon negative electrode material for a sodium ion battery, comprising the following steps:

[0012] (1) soaking bituminous coal in a mixed acid solution containing hydrochloric acid and hydrofluoric acid, rinsing until the solution is neutral, and then drying to obtain dry coal powder;

[0013] (2) mixing the theabrownin with the dry coal powder obtained in step (1), and performing a pre-oxidation treatment under an oxygen-containing atmosphere to obtain a pre-oxidation product;

[0014] (3) carbonizing the pre-oxidation product under an inert atmosphere to obtain a coal-based carbon material;

[0015] According to an embodiment of the present invention, the bituminous coal in step (1) is pre-crushed, and the particle size of the crushed bituminous coal is 45 microns to 74 microns.

[0016] According to an embodiment of the present invention, the volume ratio of hydrochloric acid to hydrofluoric acid in the mixed acid solution containing hydrochloric acid and hydrofluoric acid in step (1) is (1-4):(1-4).

[0017] According to an embodiment of the present invention, the soaking treatment time in step (1) is 5 to 48 hours.

[0018] According to an embodiment of the present invention, the mass ratio of theabrownin to dry coal powder in step (2) is (1-6):(1-6).

[0019] According to an embodiment of the present invention, the oxygen-containing atmosphere in step (2) is selected from at least one of air and oxygen.

[0020] According to an embodiment of the present invention, the inert atmosphere in step (3) is at least one of argon, nitrogen, and helium.

[0021] According to an embodiment of the present invention, the temperature of the pre-oxidation treatment in step (2) is 200-400°C.

[0022] According to an embodiment of the present invention, the pre-oxidation treatment time in step (2) is 1-12 hours.

[0023] According to an embodiment of the present invention, the carbonization temperature in step (3) is 1200-1700°C.

[0024] According to an embodiment of the present invention, the carbonization time in step (3) is 1 to 4 hours.

[0025] According to an embodiment of the present invention, the heating rate of the carbonization in step (3) is 1 to 10° C. / min.

[0026] In a second aspect of the present invention, a coal-based carbon negative electrode material for a sodium ion battery is provided, which is prepared by the preparation method described in any embodiment of the first aspect.

[0027] In a third aspect of the present invention, a sodium ion battery negative electrode is provided, comprising the coal-based carbon negative electrode material for sodium ion battery according to the second aspect.

[0028] The beneficial effects achieved by the present invention include at least:

[0029] The present invention creatively uses theabrownin containing oxygen functional groups as a regulating agent to inhibit the growth of graphite microcrystals through heterogeneous cross-linking, thereby increasing the amorphous degree and interlayer spacing of the carbon material, making it suitable for the storage of sodium ions.

[0030] The preparation method of the coal-based carbon material provided by the present invention is simple and easy to industrially produce. Through the subsequent high-temperature treatment, the twisted graphite crystallites are rearranged to form a closed-pore structure, thereby improving the initial coulombic efficiency of sodium storage in the coal-based carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the XRD pattern of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 1.

[0032] Figure 2 This is a scanning electron microscope image of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 1.

[0033] Figure 3 This is the XRD pattern of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 2.

[0034] Figure 4 This is a scanning electron microscope image of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 2.

[0035] Figure 5This is the XRD pattern of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 3.

[0036] Figure 6 This is a scanning electron microscope image of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 3.

[0037] Figure 7 This is the XRD pattern of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 4.

[0038] Figure 8 This is a scanning electron microscope image of the coal-based carbon material for the sodium ion battery negative electrode prepared in Example 4.

[0039] Figure 9 This is the XRD pattern of the coal-based carbon material for the sodium ion battery negative electrode prepared in Comparative Example 1.

[0040] Figure 10 This is a scanning electron microscope image of the coal-based carbon material for the sodium ion battery negative electrode prepared in Comparative Example 1.

[0041] Figure 11 This is the XRD pattern of the coal-based carbon material for the sodium ion battery negative electrode prepared in Comparative Example 2.

[0042] Figure 12 This is a scanning electron microscope image of the coal-based carbon material for the sodium ion battery negative electrode prepared in Comparative Example 2. DETAILED DESCRIPTION

[0043] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0044] The present invention provides a method for preparing a coal-based carbon negative electrode material for a sodium ion battery, comprising:

[0045] (1) soaking in a mixed acid solution containing hydrochloric acid and hydrofluoric acid, rinsing until the solution is neutral, and then drying to obtain dry coal powder;

[0046] (2) mixing the theabrownin with the dry coal powder obtained in step (1), and performing a pre-oxidation treatment under an oxygen-containing atmosphere to obtain a pre-oxidation product;

[0047] (3) Carbonizing the pre-oxidation product under an inert atmosphere to obtain a coal-based carbon material.

[0048] After bituminous coal is pulverized and then acid-washed, organic minerals in the coal can be removed. The acid-washed coal is mixed with the regulating agent theabrownin and pre-oxidized in an oxygen-containing atmosphere; the pre-oxidation product is carbonized at high temperature to prepare a coal-based carbon material suitable for the negative electrode of sodium ion batteries. Theabrownin contains rich oxygen-containing functional groups. Through low-temperature pre-oxidation, it constructs a heterogeneous cross-linked structure with the oxygen functional groups on the surface of bituminous coal, hindering the lateral growth and vertical stacking of carbon microcrystals, regulating the degree of disordered arrangement of microcrystals, and obtaining an amorphous hard carbon material with a large interlayer spacing and rich closed-pore structure. The resulting coal-based material has high capacity and first coulombic efficiency when used as the negative electrode of carbon sodium ion batteries. The first coulombic efficiency is above 73%, preferably above 75%; the first discharge specific capacity is above 420mAh / g, preferably above 440mAh / g.

[0049] The bituminous coal referred to herein is a type of coal with a medium degree of coalification, a carbon content of 80% to 90%, a hydrogen content of 4% to 6%, and an oxygen content of 10% to 15%. Bituminous coal has a range of metamorphic degrees, and the term "bituminous coal" as used herein encompasses all degrees of metamorphicity. The bituminous coal may be pre-ground using techniques and equipment known in the art, preferably using one or more of a jet mill, roller mill, mechanical mill, or ball mill.

[0050] According to a specific embodiment, the volume ratio of hydrochloric acid to hydrofluoric acid in the provided mixed acid solution is 1 to 4:1 to 4. The time for the mixed acid immersion treatment is 5 to 48 hours.

[0051] When mixing theabrownin with dry coal powder, mechanical equipment with high shear force commonly used in the art can be used, such as a fusion machine or a kneader, etc. According to a specific embodiment, the mixing mass ratio of theabrownin and dry coal powder is 1-10:1-10. According to a preferred embodiment, the mixing ratio of theabrownin and dry coal powder is 1-6:1-6. According to a preferred embodiment, the mixing ratio of theabrownin and dry coal powder is (1-2):(2-5), for example, (1-1.5):(2.5-5).

[0052] The oxygen-containing atmosphere mentioned may refer to one or more of air, oxygen and ozone, such as air, for convenience and cost control. The oxygen content of the oxygen-containing atmosphere mentioned may be 20% to 100%. According to a specific embodiment, the oxygen-containing atmosphere used in the pre-oxidation treatment includes air and pure oxygen, the pre-oxidation temperature is 200 to 400°C (according to a preferred embodiment, 270 to 350 degrees Celsius), and the pre-oxidation time is 1 to 12 hours (according to a preferred embodiment, 6 to 12 hours).

[0053] According to a specific embodiment, the inert atmosphere used in the carbonization of the pre-oxidation product is any one of argon, nitrogen, helium, or a combination of the two, the heating rate is 1 to 10°C / min, the carbonization temperature is 1200 to 1700°C (1400 to 1500°C according to a preferred embodiment), and the carbonization time is 1 to 4 hours.

[0054] The prepared coal-based carbon material is an amorphous hard carbon material.

[0055] The above method can be used to prepare a coal-based carbon material, wherein the interlayer spacing of the coal-based carbon material is 0.377 to 0.383 nm.

[0056] The prepared coal-based carbon material can be used as a negative electrode material for sodium-ion batteries to prepare a negative electrode for a sodium-ion battery. The negative electrode material can be applied to the surface of a negative electrode current collector to prepare a negative electrode. Methods commonly used in the art, such as coating methods, can be used to coat the provided sodium-ion battery negative electrode material on a current collector to form the negative electrode. The current collector used can be a conventional material in the art. Furthermore, the negative electrode and positive electrode, a separator, and an electrolyte can be assembled into a sodium-ion secondary battery.

[0057] The protection scheme of the present invention is described below by specific examples. It should be noted that these examples are only used to facilitate the understanding of those skilled in the art and should not be regarded as limiting the scope of protection of the present invention. Unless otherwise stated, the reagents used in the examples can be obtained commercially.

[0058] Example 1

[0059] Example 1 provides a coal-based carbon material for a negative electrode of a sodium ion battery, which is prepared by the following method:

[0060] (1) 5 g of bituminous coal was ground and immersed in a mixed solution of hydrochloric acid and hydrofluoric acid in a volume ratio of 1:1 for 24 h. The acid-treated bituminous coal powder was rinsed with deionized water until neutral and the powder was dried.

[0061] (2) 0.5 g of theabrownin was mixed with the dry coal powder obtained in step (1), and then pre-oxidized at 300° C. for 9 h in an air atmosphere.

[0062] (3) The pre-oxidation product obtained in step (2) is placed in a tubular furnace, and under an argon atmosphere, the temperature is raised to 1400°C at a rate of 5°C / min and kept constant for 2 hours to prepare a coal-based carbon sodium ion battery negative electrode material.

[0063] After characterization, the prepared coal-based carbon layer spacing is 0.383nm. As the negative electrode of sodium ion battery, the first discharge specific capacity is 439.78mAh / g at a current density of 0.1A / g.-1 , the first coulombic efficiency is 75.8%.

[0064] Example 2

[0065] Example 2 provides a coal-based carbon material for a negative electrode of a sodium ion battery, which is prepared by the following method:

[0066] (1) 5 g of bituminous coal was ground and immersed in a mixed solution of hydrochloric acid and hydrofluoric acid in a volume ratio of 2:1 for 12 h. The acid-treated bituminous coal powder was rinsed with deionized water until neutral and the powder was dried.

[0067] (2) 1.5 g of theabrownin was mixed with the dry coal powder obtained in step (1), and then pre-oxidized at 330° C. for 6 h in an oxygen atmosphere;

[0068] (3) The pre-oxidation product obtained in step (2) is placed in a tubular furnace, and the temperature is raised to 1300° C. at a rate of 6° C. / min under a nitrogen atmosphere, and the temperature is kept constant for 3 hours to prepare a coal-based carbon sodium ion battery negative electrode material.

[0069] After characterization, the prepared coal-based carbon layer spacing is 0.379nm. As the negative electrode of sodium ion battery, the first discharge capacity is 420mAh / g at a current density of 0.1A / g. -1 , the first coulombic efficiency is 74%.

[0070] Example 3

[0071] Example 3 provides a coal-based carbon material for a negative electrode of a sodium ion battery, which is prepared by the following method:

[0072] (1) 4 g of bituminous coal was ground and immersed in a mixed solution of hydrochloric acid and hydrofluoric acid in a volume ratio of 3:1 for 18 h. The acid-treated bituminous coal powder was rinsed with deionized water until neutral and the powder was dried.

[0073] (2) 1.2 g of theabrownin was mixed with the dry coal powder obtained in step (1), and then pre-oxidized at 270° C. for 12 h under an oxygen atmosphere;

[0074] (3) The pre-oxidation product obtained in step (2) is placed in a tubular furnace, and the temperature is raised to 1500° C. at a rate of 3° C. / min under an argon atmosphere, and the temperature is kept constant for 1 hour to prepare a coal-based carbon sodium ion battery negative electrode material.

[0075] After characterization, the prepared coal-based carbon layer spacing is 0.377nm. As the negative electrode of sodium ion battery, the first discharge capacity is 497mAh / g at a current density of 0.1A / g. -1 , the first coulombic efficiency is 78%.

[0076] Example 4

[0077] Example 4 provides a coal-based carbon material for a negative electrode of a sodium ion battery, which is prepared by the following method:

[0078] (1) 5 g of bituminous coal was pulverized and soaked in a 1:1 volume ratio of hydrochloric acid to hydrofluoric acid solution for 12 h. The acid-treated bituminous coal powder was rinsed with deionized water until neutral and the powder was dried.

[0079] (2) 2.0 g of theabrownin was mixed with the dry coal powder obtained in step (1), and then pre-oxidized at 325° C. for 7 h in an air atmosphere;

[0080] (3) The pre-oxidation product obtained in step (2) is placed in a tubular furnace, and the temperature is raised to 1500°C at a rate of 4°C / min under a nitrogen atmosphere, and the temperature is kept constant for 1 hour to prepare a coal-based carbon sodium ion battery negative electrode material.

[0081] The interlayer spacing of the prepared coal-based carbon was characterized to be 0.381 nm. As the negative electrode of the sodium ion battery, the first discharge capacity was 444 mAh / g at a current density of 0.1 A / g. -1 , the first coulombic efficiency is 75%.

[0082] Comparative Example 1

[0083] Comparative Example 1 provides a coal-based carbon material for a negative electrode of a sodium ion battery, which is prepared by the following method:

[0084] (1) 5 g of bituminous coal was ground and soaked in a 1:1 volume ratio of hydrochloric acid to hydrofluoric acid solution for 24 h. The acid-treated bituminous coal powder was rinsed with deionized water until neutral and the powder was dried.

[0085] (2) The above-mentioned coal powder was heated to 1400°C at a rate of 5°C / min under an argon atmosphere and kept at this temperature for 2 hours to prepare a coal-based carbon sodium ion battery negative electrode material.

[0086] After characterization, the prepared coal-based carbon layer spacing is 0.368nm. As the negative electrode of sodium ion battery, the first discharge capacity is 340mAh / g at a current density of 0.1A / g. -1 , the first coulombic efficiency is 63%.

[0087] Comparative Example 2

[0088] Comparative Example 2 provides a coal-based carbon material for a negative electrode of a sodium ion battery, which is prepared by the following method:

[0089] (1) 5 g of bituminous coal was ground and soaked in a 1:1 volume ratio of hydrochloric acid to hydrofluoric acid solution for 24 h. The acid-treated bituminous coal powder was rinsed with deionized water until neutral and the powder was dried.

[0090] (2) pre-oxidizing the dry pulverized coal obtained in step (1) at 300° C. in an air atmosphere for 9 h;

[0091] (3) The pre-oxidation product obtained in step (2) was heated to 1400°C at a rate of 5°C / min under an argon atmosphere and kept at this temperature for 2 hours to prepare a coal-based carbon sodium ion battery negative electrode material.

[0092] After characterization, the prepared coal-based carbon layer spacing is 0.373nm. As the negative electrode of sodium ion battery, the first discharge capacity is 419mAh / g at a current density of 0.1A / g. -1 , the first coulombic efficiency is 68%.

[0093] It is not difficult to see from the above embodiments and comparative examples that the method provided by the present invention can improve coal-based carbon materials with poor sodium storage performance, and further improve the reversible specific capacity and first-cycle coulombic efficiency of coal-based carbon materials.

[0094] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed process equipment and process flow of the present invention. However, the present invention is not limited to the above-described detailed process equipment and process flow, and does not necessarily rely on the above-described detailed process equipment and process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for the raw materials of the present invention's products, additions of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

[0095] In this specification, reference to terms such as "one embodiment," "some embodiments," or "specific implementations" means that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example.

[0096] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a coal-based carbon negative electrode material for a sodium ion battery, characterized in that: include: (1) Soaking the bituminous coal in a mixed acid solution containing hydrochloric acid and hydrofluoric acid, rinsing until the solution becomes neutral, and then drying to obtain dry coal powder; (2) mixing the theabrownin with the dry coal powder obtained in step (1), and performing a pre-oxidation treatment in an oxygen-containing atmosphere to obtain a pre-oxidation product; (3) Carbonizing the pre-oxidation product under an inert atmosphere to obtain a coal-based carbon material.

2. The preparation method according to claim 1, characterized in that The bituminous coal in step (1) is pre-crushed, and the particle size of the crushed bituminous coal is 45 microns to 74 microns.

3. The preparation method according to claim 1, characterized in that The volume ratio of hydrochloric acid to hydrofluoric acid in the mixed acid solution containing hydrochloric acid and hydrofluoric acid in step (1) is (1-4): (1-4); The soaking time in step (1) is 5 to 48 hours.

4. The preparation method according to claim 1, characterized in that The mass ratio of theabrownin and dry coal powder in step (2) is (1-6): (1-6).

5. The preparation method according to claim 1, characterized in that The oxygen-containing atmosphere in step (2) is selected from at least one of air, oxygen, and ozone; The inert atmosphere in step (3) is at least one of argon, nitrogen, and helium.

6. The preparation method according to claim 1, characterized in that The temperature of the pre-oxidation treatment in step (2) is 200-400°C; The pre-oxidation treatment time in step (2) is 1-12 hours.

7. The preparation method according to claim 1, characterized in that The carbonization temperature in step (3) is 1200-1700°C; The carbonization time in step (3) is 1 to 4 hours; The heating rate of the carbonization in step (3) is 1-10°C / min.

8. A coal-based carbon negative electrode material for sodium ion batteries, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. A sodium ion battery negative electrode, characterized in that Including the coal-based carbon negative electrode material for sodium ion batteries as described in claim 8.

10. A sodium ion battery, characterized in that: Including the sodium ion battery negative electrode according to claim 9.

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