Preparation method for increasing closed pore structure of coal-based hard carbon material

Abstract

The invention relates to the technical field of sodium ion battery materials, in particular to a preparation method for increasing a closed pore structure of a coal-based hard carbon material. The invention discloses a preparation method for increasing a closed pore structure of a coal-based hard carbon material. The preparation method comprises the following steps: step 1, preparing a precursor; a coal base and a magnesium ion doping source are ground, stirred and mixed through a ball mill, and a mixture is obtained; then pressing the mixture into blocks to obtain a blocky mixture; step 2, high-pressure pre-oxidation; applying pressure to heat the blocky mixture in an inert gas environment; step 3, pickling; soaking the product subjected to high-pressure pre-oxidation in acid liquor, washing the product with deionized water until the product is neutral, and drying the product; 4, high-temperature preparation; and continuously roasting at high temperature in a high-temperature furnace. According to the method, magnesium ion doping, high-pressure briquetting, pre-oxidation, acid pickling for neutralization of acid-base property and high-temperature firing are carried out in sequence to obtain the coal-based hard carbon with more closed-cell structures at first, then high-pressure briquetting and pre-oxidation are carried out, and finally, the coal-based hard carbon with more closed-cell structures is obtained.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials technology, specifically to a method for preparing coal-based hard carbon materials with increased closed-pore structure. Background Technology

[0002] Hard carbon is a primary material for sodium-ion batteries. Currently, there are three main production processes: biomass, resin-based, and coal-based. The biomass process suffers from difficulties in maintaining batch-to-batch stability of raw materials, and as sodium-ion batteries pass the initial market development stage and the market expands, insufficient domestic raw material supply and reliance on imports could restrict development. The resin-based process has higher raw material costs, which is unfavorable for the large-scale application of hard carbon in the long run.

[0003] my country has abundant, widely distributed, and inexpensive coal resources, providing a stable source of raw materials for coal-based production routes. Furthermore, the simple production process makes it suitable for the large-scale application of hard carbon. However, traditional coal-based processes suffer from low capacity and low initial coulombic efficiency in producing hard carbon. The core reason for this is the tendency for carbon materials to undergo excessive graphitization, resulting in a low proportion of closed-cell structures. Closed-cell structures are crucial for sodium storage, and graphitization hinders sodium storage, thus limiting the initial development of coal-based production routes.

[0004] Therefore, it is essential to study a method for preparing coal-based hard carbon materials with a closed-pore structure to improve the capacity of hard carbon. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems in the prior art and provide a method for preparing coal-based hard carbon materials with increased closed-pore structure, inhibiting excessive graphitization of carbon materials, increasing the formation of closed-pore structure during carbonization, thereby enhancing the low-potential sodium storage capacity and improving the capacity of hard carbon. The specific technical solution is as follows: A method for preparing coal-based hard carbon materials with increased closed-pore structure includes the following steps: Step 1: Precursor preparation; Coal-based and magnesium ion doping sources in a mass ratio of 6:4 to 8:2 are ground and mixed by ball milling to obtain a mixture; The mixture is then pressed into blocks to obtain a block mixture; Step 2: High-pressure pre-oxidation; the block mixture is heated under pressure in an inert gas environment; Step 3: Pickling; Immerse the pre-oxidized product under high pressure in acid solution, wash with deionized water until neutral and dry; Step 4: High-temperature preparation; continuous high-temperature roasting in a high-temperature furnace to obtain coal-based hard carbon with a closed-cell structure.

[0006] Preferably, the magnesium ion doping source is selected from magnesium nitrate, magnesium chloride, magnesium sulfate, or magnesium gluconate; the coal base is selected from anthracite or lignite.

[0007] Preferably, the pressing pressure in step 1 is 3-7 MPa; the grinding speed of the ball mill is 400-500 r / min, and the grinding time is 2-4 hours.

[0008] Preferably, the inert gas is selected from nitrogen, helium, or argon.

[0009] Preferably, the heating environment in step 2 is a temperature of 400℃-600℃, a pressure of 0.2-0.5Mpa, and a time of 2-6 hours.

[0010] Preferably, the acid solution is any one of dilute hydrochloric acid, dilute sulfuric acid, and phosphoric acid; the acid solution is dilute hydrochloric acid, dilute sulfuric acid, or phosphoric acid with a mass fraction of 0.8-1.2 mol / L, and the soaking time is 3-8 hours.

[0011] Preferably, the high-temperature roasting temperature in step 4 is 900℃-1500℃; the high-temperature roasting time is 3-8h.

[0012] A method for preparing coal-based hard carbon materials with increased closed-pore structure produces hard carbon materials with a discharge capacity of 350-370 mAh / g and an initial coulombic efficiency of 90%-93%. Currently available commercially available hard carbon materials have capacities of 280-310 mAh / g and coulombic efficiencies ranging from 85-88%.

[0013] Compared with the closest existing technology, the technical solution provided by the present invention has the following beneficial effects: 1. The preparation method of the present invention first involves magnesium ion doping, then high-pressure pressing into blocks, followed by a pre-oxidation process, then acid washing to neutralize the acidity and alkalinity, and finally high-temperature firing to obtain coal-based hard carbon with more closed-pore structures. This inhibits the excessive graphitization of carbon materials, increases the formation of closed-pore structures in the carbonization process, thereby enhancing the low-potential sodium storage capacity and improving the capacity of hard carbon. 2. This invention incorporates magnesium ion doping to adjust the microcrystalline environment of the derived carbon. High-pressure pressing into blocks is then used to control the degree of cross-linking in the precursor, improving the etching effect of magnesium ions on the carbon layer during high-temperature, high-pressure pre-oxidation and promoting the formation of closed-pore structures. Subsequent high-temperature, high-pressure pre-oxidation inhibits the formation of graphitic structures induced by direct carbonization, as graphite structures are unfavorable for sodium storage. Subsequent acid washing removes metal ions from the material and neutralizes its alkalinity; excessive alkalinity can lead to deactivation of the adhesive solution during subsequent battery cell anode production. Finally, high-temperature sintering produces the desired high-capacity coal-based hard carbon with numerous closed-pore structures. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the hard carbon material of the present invention; Figure 2 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Please see Figure 1-2 .

[0017] Example 1 A method for preparing coal-based hard carbon materials with increased closed-pore structure includes the following steps. Step 1: Coal-based and magnesium gluconate are ground and mixed in a ball mill at a mass ratio of 6:4. The mixture is then pressed into blocks under a pressure of 6 MPa.

[0018] Step 2 involves heating the prepared block mixture at 400°C and 0.3 MPa for 6 hours in a nitrogen atmosphere.

[0019] Step 3: Immerse the pre-oxidized product under high pressure in dilute hydrochloric acid, wash with deionized water until neutral, and dry.

[0020] Step 4 involves continuous high-temperature roasting at 1000℃ for 7 hours in a high-temperature furnace to obtain coal-based hard carbon with a large number of closed-pore structures.

[0021] Electron microscopy revealed that the spatial arrangement of the crosslinking reaction led to a transformation of the morphology from a short-range porous structure to a relatively closed space. Step 1's core function lies in establishing the initial spatial arrangement basis for the crosslinking reaction through uniform mixing of the coal-based material and the magnesium ion dopant source, followed by a high-pressure agglomeration process. Step 2 achieves the directional construction of the closed-pore structure through the synergistic effect of etching and condensation. The etching of magnesium ions leads to the formation of a large-pore structure within the carbon matrix, followed by a condensation reaction catalyzed on the surface of the coal-based carbon material. This condensation reaction restricts the expansion of the pore structure and promotes the formation of closed pores. Appropriate pressure promotes the crosslinking process and avoids defects such as cracks or voids in the carbon matrix caused by excessive pressure.

[0022] Example 2 A method for preparing coal-based hard carbon materials with increased closed-pore structure includes the following steps. Step 1: Coal-based and magnesium sulfate are ground and mixed in a ball mill at a mass ratio of 7:3. The mixture is then pressed into blocks under a pressure of 5 MPa.

[0023] Step 2 involves heating the prepared block mixture at 500°C and 0.4 MPa for 5 hours in a helium atmosphere.

[0024] Step 3: Immerse the pre-oxidized product under high pressure in dilute sulfuric acid, wash with deionized water until neutral, and dry.

[0025] Step 4 involves continuous high-temperature roasting at 1100℃ in a high-temperature furnace for 6 hours to obtain coal-based hard carbon with a large number of closed-pore structures.

[0026] Example 3 A method for preparing coal-based hard carbon materials with increased closed-pore structure includes the following steps. Step 1: Coal-based and magnesium nitrate are ground and mixed in a ball mill at a mass ratio of 8:2. The mixture is then pressed into blocks under a pressure of 4 MPa.

[0027] Step 2: The prepared block mixture is heated at 600°C and 0.5 MPa for 4 hours in an argon atmosphere.

[0028] Step 3: Immerse the pre-oxidized product under high pressure in phosphoric acid, wash with deionized water until neutral, and dry.

[0029] Step 4 involves continuous high-temperature roasting at 1200℃ for 5 hours in a high-temperature furnace to obtain coal-based hard carbon with a large number of closed-pore structures.

[0030] Comparative Example 1 Hard carbon materials were prepared according to the method of Example 3, except that the coal-based and magnesium nitrate were ground and mixed in a ball mill at a mass ratio of 8:2, omitting step 1.

[0031] Comparative Example 2 Hard carbon material was prepared according to the method of Example 3, except that the 4 MPa pressure in step 1 was omitted to form a block.

[0032] In Examples 1-3 and Comparative Examples 1-2, sodium sheets were used as the negative electrode to fabricate button cells at 25°C. Initial discharge capacity and initial coulombic efficiency performance were tested, and the results are shown in Table 1.

[0033] Table 1 Test data of Examples 1-3 and Comparative Examples 1-2 As can be seen from the test data in Table 1, the sodium-ion battery anode material prepared using the method of this invention exhibits a significantly improved capacity and good initial coulombic efficiency. The hard carbon material has a discharge capacity of 350-370 mAh / g and an initial coulombic efficiency of 90%-93%. Currently available commercially available hard carbon materials have capacities of 280-310 mAh / g and coulombic efficiencies ranging from 85-88%.

[0034] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending approval.

Claims

1. A method for preparing coal-based hard carbon materials with increased closed-pore structure, characterized in that, Includes the following steps: Step 1: Precursor preparation; Coal-based and magnesium ion doping sources in a mass ratio of 6:4 to 8:2 are ground and mixed by ball milling to obtain a mixture; The mixture is then pressed into blocks to obtain a block mixture; Step 2: High-pressure pre-oxidation; the block mixture is heated under pressure in an inert gas environment; Step 3: Pickling; Immerse the pre-oxidized product under high pressure in acid solution, wash with deionized water until neutral and dry; Step 4: High-temperature preparation; continuous high-temperature roasting in a high-temperature furnace to obtain coal-based hard carbon with a closed-cell structure.

2. The method for preparing a coal-based hard carbon material with increased closed-pore structure according to claim 1, characterized in that, The magnesium ion doping source can be selected from magnesium nitrate, magnesium chloride, magnesium sulfate, or magnesium gluconate; the coal base can be selected from anthracite or lignite.

3. The method for preparing a coal-based hard carbon material with increased closed-pore structure according to claim 1, characterized in that, The pressing pressure in step 1 is 3-7 MPa; the grinding speed of the ball mill is 400-500 r / min, and the grinding time is 2-4 hours.

4. The method for preparing a coal-based hard carbon material with increased closed-pore structure according to claim 1, characterized in that, The inert gas can be any one of nitrogen, helium, or argon.

5. The method for preparing a coal-based hard carbon material with increased closed-pore structure according to claim 1, characterized in that, The heating environment in step 2 is 400℃-600℃, 0.2-0.5Mpa pressure, and 2-6h time.

6. The method for preparing a coal-based hard carbon material with increased closed-pore structure according to claim 1, characterized in that, The acid solution is any one of dilute hydrochloric acid, dilute sulfuric acid, and phosphoric acid; the acid solution is dilute hydrochloric acid, dilute sulfuric acid, or phosphoric acid with a mass fraction of 0.8-1.2 mol / L, and the soaking time is 3-8 hours.

7. The method for preparing a coal-based hard carbon material with increased closed-pore structure according to claim 1, characterized in that, In step 4, the high-temperature roasting temperature is 900℃-1500℃; the high-temperature roasting time is 3-8h.

8. The hard carbon material prepared by the method for increasing the closed-pore structure of coal-based hard carbon materials according to any one of claims 1 to 7, characterized in that, The discharge capacity of the hard carbon material is 350-370 mAh / g, and the initial coulombic efficiency is 90%-93%.

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