A method for preparing hard carbon materials using anthracite and its application

Abstract

This invention relates to a method for preparing hard carbon materials from anthracite and its application. The method for preparing hard carbon materials from anthracite provided by this invention includes ball milling anthracite lumps in a ball mill to obtain coal powder; performing heteroatom doping under a heteroatom atmosphere and a certain temperature to obtain heteroatom-doped coal powder; subjecting the ball-milled heteroatom-doped coal powder to carbon deposition treatment under a hydrocarbon atmosphere to obtain dense carbon; and subjecting the obtained dense carbon to high-temperature carbonization under an inert atmosphere to obtain hard carbon materials. This method, by introducing heteroatoms and carbon deposition treatment, improves the yield of anthracite materials prepared into hard carbon materials, and can increase the carbon interlayer spacing, promote charge transfer, and enhance the interaction between the electrode and the electrolyte, thereby improving the capacity and conductivity of the hard carbon materials. The high-quality hard carbon materials prepared can meet the requirements of sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a method for preparing hard carbon materials using anthracite and its application. Background Technology

[0002] Carbon materials possess advantages such as wide availability, abundant resources, and diverse structures. They also exhibit good conductivity, are green, safe, and environmentally friendly, making them widely used in lithium-ion batteries. Scientists have long hoped that the development of carbon materials in lithium-ion batteries could be successfully replicated in sodium-ion batteries. For example, graphite is a common anode material in lithium-ion batteries, possessing moderate lithium storage capacity. However, research shows that sodium ions cannot be well intercalated into graphite layers. Therefore, non-graphitized materials are considered the preferred anode for sodium-ion batteries. Some hard carbon materials, for instance, have attracted considerable attention from sodium-ion battery researchers due to their ability to provide a reversible capacity of 300 mAh / g.

[0003] The technological barriers to hard carbon production mainly lie in the process control and technological accumulation involved in raw material selection, cross-linking treatment, carbonization, and purification. The basic steps in preparing hard carbon anodes include pretreatment, carbonization, and purification. Depending on the characteristics of the raw materials, additional steps such as acid washing, water washing, sintering, and polycondensation curing may be added. Because the sources of precursors are not consistent, a wide range of raw materials correspond to different processes and procedures, making the production process and equipment selection for sodium-ion battery hard carbon anodes complex.

[0004] Among numerous hard carbon precursor materials suitable for large-scale production, coal has a carbon content second only to graphite, and possesses a dense structure and good orientation properties, making coal-based hard carbon materials an effective alternative to graphite. Anthracite, in particular, has a high carbon content, low volatile matter, dense structure, high hardness, and burns without smoke. However, there are few reports on the use of anthracite in preparing hard carbon materials for sodium-ion batteries. Hard carbon is currently the best sodium-ion anode material, but the biggest problem is the immaturity of precursor selection and industrial preparation processes. Anthracite is an excellent precursor material for hard carbon preparation, but a suitable process for converting anthracite into hard carbon has not yet been found. Summary of the Invention

[0005] To address the above problems, this invention proposes a method for preparing hard carbon materials using anthracite and its application.

[0006] The method for preparing hard carbon materials from anthracite provided by the present invention includes the following steps:

[0007] Step 1): The anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 200-500 mesh.

[0008] Step 2): The coal powder obtained in Step 1) is placed in a tubular furnace and doped with heteroatoms in a heterogeneous atmosphere and at a certain temperature to obtain heterogeneous coal powder. The doping temperature is 200-500℃ and the doping time is 324h.

[0009] Step 3): The mixed raw coal powder obtained in step 2) is put into a ball mill for ball milling and pulverization. The particle size of the mixed raw coal powder after ball milling is 200-500 mesh.

[0010] Step 4): The ball-milled raw coal powder from step 3) is subjected to carbon deposition treatment in a hydrocarbon atmosphere to obtain dense carbon. The carbon deposition treatment temperature is 800-1300℃ and the carbon deposition treatment time is 324h.

[0011] Step 5): The dense carbon obtained in step 4) is carbonized at high temperature under an inert atmosphere to obtain hard carbon material;

[0012] The mixed atmosphere is one or more of the following: fluoromethane, chloromethane, bromomethane, ammonia, oxygen, phosphine, phosphorus trifluoride, phosphorus pentafluoride, boron trichloride, or diborane.

[0013] The hydrocarbon atmosphere is one or more of methane, ethylene, acetylene, propane, natural gas, and toluene;

[0014] The inert atmosphere is one or more of argon, nitrogen, helium, and carbon dioxide.

[0015] Furthermore, in step 2), the doping temperature is 300℃ and the doping time is 12h.

[0016] Furthermore, in step 4), the carbon deposition treatment temperature is 1000°C and the carbon deposition treatment time is 12h.

[0017] Furthermore, in step 5), the carbonization temperature is 1500℃ and the carbonization time is 2h.

[0018] Furthermore, the heterogeneous atmosphere is fluoromethane.

[0019] Furthermore, the hydrocarbon atmosphere is methane.

[0020] Furthermore, the inert atmosphere is argon.

[0021] The hard carbon material prepared by the method described in this invention is used in sodium-ion batteries.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. The method of the present invention improves the yield of anthracite coal to hard carbon material by introducing heteroatoms (such as O, N, S, P and other elements) and carbon deposition treatment. It can also increase the carbon interlayer spacing, promote charge transfer and enhance the interaction between the electrode and the electrolyte, thereby improving the capacity and conductivity of the hard carbon material. The high-quality hard carbon material prepared can meet the requirements of sodium-ion batteries.

[0024] 2. The hard carbon material prepared by the method of the present invention can provide sodium-ion batteries with higher initial capacity, higher first-cycle coulombic efficiency and stronger capacity stability.

[0025] 3. The hard carbon material prepared by this invention exhibits excellent electrochemical performance in sodium-ion battery systems. Furthermore, it is prepared using anthracite, which is low-cost, simple to process, and can be mass-produced, thus promising to realize the large-scale development of sodium-ion battery systems. Attached Figure Description

[0026] Figure 1 Here is a SEM image of the hard carbon material prepared in Example 1;

[0027] Figure 2 This is the XRD pattern of the hard carbon material prepared in Example 1;

[0028] Figure 3 This is a graph showing the cycling performance and coulombic efficiency of sodium ions in Example 1;

[0029] Figure 4 This is a graph showing the cycling performance and coulombic efficiency of sodium ions in Example 2;

[0030] Figure 5 This is a SEM image of the hard carbon material prepared in Comparative Example 1;

[0031] Figure 6 The graph shows the cycling performance and coulombic efficiency of sodium ions in Comparative Example 1.

[0032] Figure 7 The image shows the XRD pattern of the carbon material prepared in Comparative Example 2.

[0033] Figure 8 The graph shows the cycling performance and coulombic efficiency of sodium ions in Comparative Example 2.

[0034] Figure 9 This is a graph showing the cycling performance and coulombic efficiency of sodium ions in Comparative Example 3. Detailed Implementation

[0035] The present invention will be further described below with reference to the embodiments.

[0036] Example 1: Preparation of hard carbon materials by fluorine atom doping and their application in sodium-ion batteries

[0037] The method of the present invention for preparing hard carbon materials from anthracite includes the following steps:

[0038] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0039] Step 2) The coal powder obtained in Step 1) is placed in a tubular furnace and doped with fluorine atoms at 300°C under a fluoromethane atmosphere for 12 hours to obtain fluorine-atom coal powder.

[0040] Step 3) The fluorine-atom coal powder obtained in step 2) is put into a ball mill for ball milling and pulverization. The particle size of the fluorine-atom coal powder after ball milling is 500 mesh.

[0041] Step 4) The fluorine-atom coal powder after ball milling in step 3) is subjected to carbon deposition in a methane atmosphere at 1000°C for 12 hours to obtain dense carbon.

[0042] Step 5) The dense carbon from Step 4) is carbonized at a high temperature of 1500℃ for 2 hours under an argon atmosphere to obtain a hard carbon material (see...). Figure 1 and Figure 2 The obtained hard carbon material weighed 92g, with a yield of 92%.

[0043] Step 6) The carbonized hard carbon material is prepared into a slurry according to the ratio of hard carbon: carbon black: CMC: SBR = 94: 1.5: 1.5: 3 and coated onto copper foil to obtain hard carbon electrode sheets.

[0044] The aforementioned hard carbon electrode was used as the negative electrode of the sodium-ion battery. Battery assembly was carried out in an argon-filled glove box, with the hard carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the battery underwent charge-discharge cycling at a rate of 0.1C between 0.01V and 2.5V. The initial discharge specific capacity reached 332.1 mAh / g; the first-cycle coulombic efficiency reached 89.1%, and the specific capacity remained at 87.9% after 80 cycles (see...). Figure 3 ).

[0045] The results indicate that, according to the method of the present invention, the yield of hard carbon material doped with fluorine atoms and treated with carbon deposition can reach 92%. When used in sodium-ion battery systems, it can provide sodium-ion batteries with an initial capacity of up to 332.1 mAh / g, a first-cycle coulombic efficiency of 89.1%, and a specific capacity of 87.9% after 80 cycles. The electrochemical performance is good and stable, which can meet the market demand for sodium-ion batteries.

[0046] Example 2: Preparation of hard carbon from chlorine-doped anthracite and its application in sodium-ion batteries.

[0047] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0048] Step 2) The coal powder obtained in Step 1) is placed in a tubular furnace and subjected to chlorine atom doping at 300°C under a chloromethane atmosphere for 12 hours to obtain chlorine atom coal powder.

[0049] Step 3) The chlorine-containing coal powder obtained in Step 2) is put into a ball mill for ball milling and pulverization. The particle size of the chlorine-containing coal powder after ball milling is 500 mesh.

[0050] Step 4) The chlorine-atom coal powder after ball milling in step 3) is subjected to carbon deposition in a methane atmosphere at 1000°C for 12 hours to obtain dense carbon.

[0051] Step 5) The dense carbon from Step 4 is carbonized at high temperature in an argon atmosphere. The carbonization temperature is 1500℃ and the carbonization time is 2h to obtain hard carbon material. The weight of the hard carbon material is 90g and the yield is 90%.

[0052] Step 6) The carbonized hard carbon material is prepared into a slurry according to the ratio of hard carbon: carbon black: CMC: SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain hard carbon electrode sheets;

[0053] The aforementioned hard carbon electrode was used as the negative electrode of the sodium-ion battery. Battery assembly was carried out in an argon-filled glove box, with the hard carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the battery underwent charge-discharge cycling at a rate of 0.1C between 0.01V and 2.5V. The initial discharge specific capacity reached 308.4 mAh / g; the first-cycle coulombic efficiency reached 87.6%, and the specific capacity remained at 73.5% after 80 cycles (see...). Figure 4 ).

[0054] The results indicate that, according to the method of the present invention, the yield of hard carbon material doped with chlorine atoms and treated with carbon deposition can reach 90%. When used in sodium-ion battery systems, it can provide sodium-ion batteries with an initial capacity of up to 308.4 mAh / g, a first-cycle coulombic efficiency of 87.6%, and a specific capacity of 73.5% after 80 cycles. The electrochemical performance is good and stable, which can meet the market demand for sodium-ion batteries.

[0055] Example 3: Preparation of hard carbon from bromine-doped anthracite and its application in sodium-ion batteries.

[0056] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0057] Step 2) The coal powder obtained in Step 1) is placed in a tubular furnace and subjected to bromine atom doping at 300°C under a bromomethane atmosphere for 12 hours to obtain bromine atom coal powder.

[0058] Step 3) The bromine-containing coal powder obtained in Step 2) is put into a ball mill for ball milling and pulverization. The particle size of the bromine-containing coal powder after ball milling is 500 mesh.

[0059] Step 4) The bromine-containing coal powder after ball milling in Step 3) is subjected to carbon deposition in a methane atmosphere at 1000°C for 12 hours to obtain dense carbon.

[0060] Step 5) The dense carbon from Step 4 is carbonized at high temperature in an argon atmosphere. The carbonization temperature is 1500℃ and the carbonization time is 2h to obtain hard carbon material. The weight of the hard carbon material is 91g and the yield is 91%.

[0061] Step 6) The carbonized hard carbon material is prepared into a slurry according to the ratio of hard carbon: carbon black: CMC: SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain hard carbon electrode sheets;

[0062] The aforementioned hard carbon electrode was used as the negative electrode of the sodium-ion battery. Battery assembly was carried out in an argon-filled glove box, with the hard carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the battery underwent charge-discharge cycling at a rate of 0.1C between 0.01V and 2.5V. The initial discharge specific capacity reached 298.9 mAh / g; the first-cycle coulombic efficiency reached 83.6%, and the specific capacity remained at 75.4% after 80 cycles.

[0063] The results indicate that, according to the method of the present invention, the yield of hard carbon material doped with bromine atoms and treated with carbon deposition can reach 91%. When used in sodium-ion battery systems, it can provide sodium-ion batteries with an initial capacity of up to 298.9 mAh / g, with a first-cycle coulombic efficiency of 83.6%, and a specific capacity of 75.4% after 80 cycles. The electrochemical performance is good and stable, which can meet the market demand for sodium-ion batteries.

[0064] Example 4: Preparation of hard carbon from nitrogen-doped anthracite and its application in sodium-ion batteries.

[0065] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0066] Step 2) The coal powder obtained in Step 1) is placed in a tubular furnace and subjected to nitrogen atom doping at 300°C under an ammonia atmosphere for 12 hours to obtain nitrogen atom coal powder.

[0067] Step 3) The nitrogen-atom coal powder obtained in Step 2) is put into a ball mill for ball milling and pulverization. The particle size of the nitrogen-atom coal powder after ball milling is 500 mesh.

[0068] Step 4) The nitrogen-atom coal powder after ball milling in step 3) is subjected to carbon deposition in a methane atmosphere at 1000°C for 12 hours to obtain dense carbon.

[0069] Step 5) The dense carbon from Step 4 is carbonized at high temperature in an argon atmosphere. The carbonization temperature is 1500℃ and the carbonization time is 2h to obtain hard carbon material. The weight of the hard carbon material is 93g and the yield is 93%.

[0070] Step 6) The carbonized hard carbon material is prepared into a slurry according to the ratio of hard carbon: carbon black: CMC: SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain hard carbon electrode sheets;

[0071] The aforementioned hard carbon electrode was used as the negative electrode of the sodium-ion battery. Battery assembly was carried out in an argon-filled glove box, with the hard carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 vL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the battery underwent charge-discharge cycling at a rate of 0.1C between 0.01V and 2.5V. The initial discharge specific capacity reached 318.7 mAh / g; the first-cycle coulombic efficiency reached 87.8%, and the specific capacity remained at 85.4% after 80 cycles.

[0072] The results indicate that, according to the method of the present invention, the yield of hard carbon material doped with nitrogen atoms and treated with carbon deposition can reach 93%. When used in sodium-ion battery systems, it can provide sodium-ion batteries with an initial capacity of up to 318.7 mAh / g, with a first-cycle coulombic efficiency of 87.8%, and a specific capacity of 85.4% after 80 cycles. The electrochemical performance is good and stable, which can meet the market demand for sodium-ion batteries.

[0073] Example 5: Preparation of hard carbon from phosphorus-doped anthracite and its application in sodium-ion batteries.

[0074] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0075] Step 2) The coal powder obtained in Step 1) is placed in a tube furnace and subjected to phosphorus atom doping at 300°C under a phosphine atmosphere for 12 hours to obtain phosphorus atom coal powder.

[0076] Step 3) The phosphorus-containing coal powder obtained in Step 2) is put into a ball mill for ball milling and pulverization. The particle size of the phosphorus-containing coal powder after ball milling is 500 mesh.

[0077] Step 4) The ball-milled phosphorus-atom coal powder from step 3) is subjected to carbon deposition in a methane atmosphere at 1000°C for 12 hours to obtain dense carbon.

[0078] Step 5) The dense carbon from Step 4 is carbonized at high temperature in an argon atmosphere. The carbonization temperature is 1500℃ and the carbonization time is 2h to obtain hard carbon material. The weight of the hard carbon material is 91g and the yield is 91%.

[0079] Step 6) The carbonized hard carbon material is prepared into a slurry according to the ratio of hard carbon: carbon black: CMC: SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain hard carbon electrode sheets;

[0080] The aforementioned hard carbon electrode was used as the negative electrode of the sodium-ion battery. Battery assembly was carried out in an argon-filled glove box, with the hard carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the battery underwent charge-discharge cycling at a rate of 0.1C between 0.01V and 2.5V. The initial discharge specific capacity reached 310.2 mAh / g; the first-cycle coulombic efficiency reached 87.6%, and the specific capacity remained at 86.4% after 80 cycles.

[0081] The results indicate that, according to the method of the present invention, the yield of hard carbon material doped with phosphorus atoms and treated with carbon deposition can reach 91%. When used in sodium-ion battery systems, it can provide sodium-ion batteries with an initial capacity of up to 310.2 mAh / g, with a first-cycle coulombic efficiency of 87.6%, and a specific capacity of 86.4% after 80 cycles. The electrochemical performance is good and stable, which can meet the market demand for sodium-ion batteries.

[0082] As can be seen from Example 15, the technical solution of the present invention exhibits the following patterns:

[0083] (1) Before preparing hard carbon materials from anthracite, doping with fluorine, chlorine, bromine, nitrogen and phosphorus atoms can affect the conductivity and number of defects of hard carbon materials, and ultimately improve the sodium storage performance of hard carbon materials obtained from anthracite.

[0084] (2) Halogen doping, nitrogen atom doping, phosphorus atom doping, as well as sulfur atom, boron atom, oxygen atom, etc. can all improve the structural properties of hard carbon materials. However, at high temperatures, these heteroatoms have greater escape, which will weaken the doping effect. The CF bond has the strongest binding force, so fluorine atom doping has the best effect.

[0085] (3) Hard carbon materials that are doped with fluorine atoms and then deposited together with carbon atoms can form CF bonds and expand the carbon layer spacing of hard carbon materials. Due to defective electrons, sodium ions can be inserted / extracted more quickly, which ultimately improves the electrochemical performance of the material and enhances the performance of sodium-ion batteries.

[0086] Example 6: Comparative experiment on the preparation of hard carbon materials by carbon deposition under different hydrocarbon atmospheres with fluorine atom doping and their application in sodium-ion batteries.

[0087] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0088] Step 2) The coal powder obtained in Step 1) is placed in a tubular furnace and doped with fluorine atoms at 300°C under a fluoromethane atmosphere for 12 hours to obtain fluorine-atom coal powder.

[0089] Step 3) The fluorine-atom coal powder obtained in step 2) is put into a ball mill for ball milling and pulverization. The particle size of the fluorine-atom coal powder after ball milling is 500 mesh.

[0090] Step 4) The fluorine-atom coal powder after ball milling in Step 3) is subjected to carbon deposition at 1000℃ under different carbon hydrocarbon atmospheres for 3-12 hours to obtain dense carbon; (see Table 1 for carbon hydrocarbon atmosphere and carbon deposition time).

[0091] Step 5) The dense carbon from step 4 is carbonized at high temperature in an argon atmosphere. The carbonization temperature is 1500℃ and the carbonization time is 2h to obtain hard carbon material.

[0092] Step 6) The carbonized hard carbon material is prepared into a slurry according to the ratio of hard carbon: carbon black: CMC: SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain hard carbon electrode sheets;

[0093] The aforementioned hard carbon electrode was used as the negative electrode of the sodium-ion battery. Battery assembly was performed in an argon-filled glove box, with the hard carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly, the batteries were allowed to stand at 25°C for 8 hours, followed by charge-discharge cycling at 0.1C between 0.01V and 2.5V.

[0094] Table 1. Comparative experiments on the preparation of hard carbon materials by carbon deposition under different hydrocarbon atmospheres with fluorine atom doping and their application in sodium-ion batteries.

[0095]

[0096]

[0097] The above experiments show that, under the premise of fluorine atom doping, the carbon deposition process using hydrocarbon gas according to this invention has the following effects on the preparation of hard carbon materials and the performance of sodium-ion batteries:

[0098] (1) Carbon hydrocarbon gas will decompose into gaseous hydrogen and solid carbon black under high temperature pyrolysis. The hydrogen produced by pyrolysis will react with the impurity elements contained in the anthracite at high temperature to generate impurity gas (CO2, CO, etc.) and be discharged to remove impurities. Solid carbon black is used as a filler to fill the pores of the anthracite to control the specific surface area and reduce defects. Therefore, carbon deposition treatment after doping anthracite with carbon hydrocarbon gas can improve the hard carbon yield.

[0099] (2) The carbon black produced by cracking different hydrocarbon gases varies greatly, and the impact on hard carbon materials differs significantly. The more complex the types of hydrocarbons in the hydrocarbon gas, the more complex the carbon black generation process, which will lead to uneven carbon black particle size and poor structure, making it a poor filler and ultimately resulting in insufficient carbon deposition and poor quality of hard carbon materials. These hydrocarbon gases include natural gas, ethylene (cracked into various hydrocarbon gases), acetylene (cracked into various hydrocarbon gases), etc. Aromatic hydrocarbons generate carbon black quickly, in a short time, and in greater quantities, but the generated carbon black particles will be larger, making it less effective at filling the micropores in anthracite, ultimately resulting in surface coating of carbon materials and poorer hard carbon performance. Such hydrocarbon gases include aromatic hydrocarbon gases such as toluene. In summary, carbon black from methane cracking is the best. Using methane as a hydrocarbon gas results in the highest hard carbon yield and the best performance in sodium-ion batteries.

[0100] (3) The carbon black produced by the cracking of hydrocarbon gas has a stable crystal structure and a large number of micropores, which can store sodium ions, enabling the battery to exhibit good cycle performance and capacity reversibility. However, the presence of too much carbon black will lead to a lower initial coulombic efficiency, affecting the performance of hard carbon materials. Therefore, there is a limit to carbon deposition. Specifically, in this embodiment, it can be seen that the optimal temperature for carbon deposition treatment with methane as the hydrocarbon gas is 1000℃, and the carbon deposition treatment time is 12h. The hard carbon material obtained in the end has a significantly different effect on sodium-ion batteries compared with other treatment groups.

[0101] Comparative Example 1: Preparation of carbon materials by direct high-temperature carbonization of anthracite and their application in sodium-ion batteries

[0102] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0103] Step 2) The coal powder from Step 1) is carbonized at high temperature under an argon atmosphere. The carbonization temperature is 1500℃ and the carbonization time is 2 hours to obtain carbon material (see...). Figure 5 The carbon material weighed 74g, with a yield of 74%.

[0104] Step 3) The carbonized carbon material is prepared into a slurry according to the ratio of carbon:carbon black:CMC:SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain carbon electrode sheets;

[0105] The aforementioned hard carbon electrode was used as the negative electrode for sodium-ion batteries. Battery assembly was performed in an argon-filled glove box, with the carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the batteries underwent charge-discharge cycling at a rate of 0.1C between 0.01V and 2.5V. The initial discharge specific capacity was 219.4 mAh / g; the first-cycle coulombic efficiency was 57.1%, and the specific capacity remained at 47.0% after 80 cycles (see...). Figure 6 ).

[0106] from Figure 5 It is evident that the carbon material obtained in this comparative example has a relatively large number of pores, indicating that there is room for carbon deposition treatment. However, the carbon material prepared directly from anthracite in this comparative example, without heteroatom doping and carbon deposition treatment, cannot suppress the graphitization of anthracite at high temperatures. This results in not only a low carbon material yield but also an inability to control the formation of high-quality hard carbon material, leading to poor electrochemical performance. Consequently, the first-cycle specific capacity, first-cycle coulombic efficiency, and capacity retention are all relatively low when applied to sodium-ion batteries, failing to meet the requirements of sodium-ion batteries.

[0107] Comparative Example 2: Preparation of carbon materials and their application in sodium-ion batteries using carbon deposition without heteroatom doping.

[0108] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0109] Step 2) The ball-milled coal powder from Step 1) is subjected to carbon deposition in a methane atmosphere at 1000°C for 12 hours to obtain dense carbon.

[0110] Step 3) The dense carbon from Step 2) is carbonized at high temperature in an argon atmosphere at 1500℃ for 2 hours to obtain carbon material (XRD pattern shown). Figure 7 The carbon material weighed 89g, with a yield of 89%.

[0111] Step 4) The carbonized carbon material is prepared into a slurry according to the ratio of carbon:carbon black:CMC:SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain carbon electrode sheets;

[0112] The aforementioned carbon electrode was used as the negative electrode in a sodium-ion battery. Battery assembly was performed in an argon-filled glove box, with the carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the battery underwent charge-discharge cycling at 0.1C between 0.01V and 2.5V. The initial discharge specific capacity was 198.9 mAh / g; the first-cycle coulombic efficiency was 77.9%, and the specific capacity remained at 65.4% after 80 cycles (see...). Figure 8 ).

[0113] Figure 7 The XRD pattern shows that the carbon material obtained by this method contains both hard carbon and soft carbon, and the formation of hard carbon cannot be effectively controlled. This indicates that using carbon deposition without heteroatom doping treatment cannot suppress the graphitization of anthracite at high temperatures. The resulting material is not a high-quality pure hard carbon material, and its electrochemical performance is poor. The first-cycle specific capacity, first-cycle coulombic efficiency, and capacity retention are all relatively low when applied to sodium-ion batteries, which cannot meet the requirements of sodium-ion batteries. In particular, the first-cycle discharge specific capacity is 198.9 mAh / g, which is even lower than that of hard carbon materials without carbon deposition process.

[0114] Comparative Example 3: A comparative experiment on the preparation of hard carbon materials using fluorine atom doping without carbon deposition and their application in sodium-ion batteries.

[0115] Step 1) 100g of anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 500 mesh;

[0116] Step 2) The coal powder obtained in Step 1) is placed in a tubular furnace and subjected to oxygen atom doping at 300°C under a fluoromethane atmosphere for 12 hours to obtain fluorine atom coal powder.

[0117] Step 3) The fluorine-atom coal powder obtained in step 2) is put into a ball mill for ball milling and pulverization. The particle size of the fluorine-atom coal powder after ball milling is 500 mesh.

[0118] Step 4) The fluorine-atom coal powder obtained in Step 3) is subjected to high-temperature carbonization in an argon atmosphere. The carbonization temperature is 1500℃ and the carbonization time is 2h to obtain hard carbon material. The weight of the hard carbon material is 71g and the yield is 71%.

[0119] Step 5) The carbonized hard carbon material is prepared into a slurry according to the ratio of hard carbon: carbon black: CMC: SBR = 94:1.5:1.5:3 and coated onto copper foil to obtain hard carbon electrode sheets;

[0120] The aforementioned hard carbon electrode was used as the negative electrode of the sodium-ion battery. Battery assembly was carried out in an argon-filled glove box, with the hard carbon electrode, glass fiber, and sodium sheet serving as the working electrode, separator, and counter electrode, respectively. A conventional electrolyte (100 μL) was added to each battery; the conventional electrolyte was a mixture of EC and DMC (1:1, v / v). After assembly and resting at 25°C for 8 hours, the battery underwent charge-discharge cycling at a rate of 0.1C between 0.01V and 2.5V. The initial discharge specific capacity was 293.1 mAh / g; the first-cycle coulombic efficiency was 72.9%, and the specific capacity remained at 41.7% after 80 cycles (see...). Figure 9 ).

[0121] The results indicate that while the method of preparing hard carbon materials from anthracite using fluorine atom doping without carbon deposition can produce hard carbon, the yield is low and defects are large due to the inability to control the specific surface area of ​​the hard carbon. Ultimately, this results in poor electrochemical performance, with low first-cycle specific capacity, first-cycle coulombic efficiency, and capacity retention in sodium-ion batteries. In particular, the first-cycle coulombic efficiency is 72.9%, and the specific capacity remains at 41.7% after 80 cycles, which cannot meet the requirements of sodium-ion batteries.

[0122] In summary, the method for preparing hard carbon materials from anthracite provided by this invention uses heteroatom doping combined with carbon deposition, which can reduce the problems of large specific surface area and many defects in hard carbon materials. This results in improved coulombic efficiency when hard carbon materials are applied to sodium-ion batteries, meeting the requirements for hard carbon materials applicable to sodium-ion batteries.

[0123] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0124] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a hard carbon material as a sodium-ion electronic anode from anthracite coal, characterized by, Includes the following steps: Step 1): The anthracite lumps are ball-milled in a ball mill to obtain coal powder with a particle size of 200-500 mesh; Step 2): The coal powder obtained in Step 1) is placed in a tubular furnace and doped with heteroatoms in a heterogeneous atmosphere and at a certain temperature to obtain heterogeneous coal powder. The doping temperature is 300℃ and the doping time is 12h. Step 3): The mixed raw coal powder obtained in Step 2) is put into a ball mill for ball milling and pulverization. The particle size of the mixed raw coal powder after ball milling is 200-500 mesh. Step 4): The ball-milled raw coal powder from Step 3) is subjected to carbon deposition treatment in a hydrocarbon atmosphere to obtain dense carbon. The carbon deposition treatment temperature is 1000℃ and the carbon deposition treatment time is 12h. Step 5): The dense carbon obtained in Step 4) is carbonized at high temperature in an inert atmosphere to obtain hard carbon material; The original atmosphere is fluoromethane; The hydrocarbon atmosphere is methane; The inert atmosphere is argon.

2. The application of the hard carbon material prepared by the method according to claim 1 in sodium-ion batteries.

Images