Carbon negative electrode material and preparation method thereof, and sodium ion battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a carbon negative electrode material, a preparation method thereof and a sodium ion battery. Compared with the prior art, the carbon negative electrode material is prepared by secondary carbonization, and anthracite is used as a precursor. Different carbon-coating sources are introduced to coat anthracite with carbon, and then a carbon deposition process is performed. Finally, high-temperature carbonization is performed to obtain the carbon negative electrode material. The preparation method has the advantages of less raw reagents, easy control of synthesis process conditions, simple operation, low temperature, low energy consumption, high yield and easy industrial production.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a carbon anode material and its preparation method, and a sodium-ion battery. Background Technology

[0002] The development of renewable energy and large-scale energy storage systems is considered an effective way to solve the current energy crisis. Although lithium-ion batteries have been proven in many fields such as automobiles and portable electronic devices, the uneven distribution of lithium mineral resources has posed a significant constraint on large-scale stationary energy storage. As an alternative, sodium-ion batteries have attracted increasing attention due to their cost-effectiveness and similar chemical properties to lithium. Sodium-ion batteries are a new type of rechargeable battery that can complement lithium-ion batteries in some areas. Sodium is an abundant element in the Earth's crust, more widely distributed and cheaper than lithium, thus sodium-ion batteries have greater resource sustainability and economic viability. In addition, sodium-ion batteries have a high energy density, which is expected to meet the future growth in energy demand. Therefore, sodium-ion batteries are considered an energy storage technology with great development potential. However, sodium-ion batteries still face challenges in terms of cycle life, energy density, and safety. The cycle stability of existing sodium-ion battery materials is not high, and the stability of the electrolyte also needs further improvement. Therefore, the research focus of sodium-ion batteries is mainly on material design, electrolyte optimization, and interface engineering to improve their cycle stability and energy density, and further promote their commercial application.

[0003] Carbon materials are currently the primary anode materials for sodium-ion batteries due to their abundant availability and low cost. Among them, hard carbon, with its large interlayer spacing and numerous lattice defects, allows for the deposition of more Na+. + Anthracite, which can be intercalated into carbon layers, has attracted considerable attention. Polymers, resins, and carbon-containing compounds are often used as precursors for hard carbon because they offer high sodium storage capacity, thus attracting researchers' interest. However, since sodium ions are consumed at defects in the material to form a stable solid electrolyte interface (SEI) film, this often sacrifices the initial coulombic efficiency (ICE). Therefore, developing low-cost, high ICE, and high-capacity hard carbon has become particularly important. Anthracite is a promising precursor for carbon materials due to its abundant resources, low cost, high carbon yield, and low impurity content. Unfortunately, anthracite-derived carbon typically has abundant surface defects, which significantly affects the ICE.

[0004] In order to optimize and adjust the microcrystalline structure and pore structure of hard carbon materials, Chinese Patent No. CN112645305A discloses a method for preparing anthracite-based hard carbon materials by combining pre-activation pore-forming and high-temperature carbonization, including the following steps: (1) Grinding and screening: crushing and screening raw coal to obtain powder of the target particle size; (2) Pre-activation: mixing the powder with the activation gas or activator, and heating it to 700-1000℃ at a heating rate of 2-20℃ / min under an inert atmosphere, and holding it for 1-6h to obtain the pre-activated product; (3) Carbonization: heating the pre-activated product to 800-1800℃ at a heating rate of 2-20℃ / min under an inert atmosphere, and holding it for 0.5-10h to obtain the anthracite-based hard carbon material. When hard carbon materials are used as anodes in sodium-ion batteries, the reversible capacity is 154.7 mAh / g at 0.1C (1C = 300 mA / g), and the initial coulombic efficiency is 73%. However, the preparation method is complex, and the obtained electrochemical performance still needs improvement. Therefore, the research on hard carbon anodes for sodium-ion batteries has attracted increasing attention from researchers and industries both domestically and internationally, and exploring a highly efficient sodium-ion anode material is urgently needed. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a carbon anode material and its preparation method, and a sodium-ion battery, wherein the carbon material, as an anode material for sodium-ion batteries, has a high initial coulombic efficiency.

[0006] This invention provides a method for preparing carbon materials, comprising the following steps:

[0007] S1) Anthracite is treated to remove impurities, resulting in anthracite with impurities removed;

[0008] S2) Grind the anthracite coal after removing impurities to obtain ground anthracite coal;

[0009] S3) The ground anthracite is passed through a carbon hydrocarbon gas in a protective atmosphere and carbon is coated by chemical vapor deposition to obtain carbon-coated coal powder.

[0010] S4) The carbon-coated coal powder is carbonized at high temperature in a protective atmosphere to obtain carbon material.

[0011] Preferably, in step S2), an organic carbon source is added during grinding, followed by pyrolysis to obtain ground anthracite.

[0012] Preferably, the mass ratio of the anthracite coal to the organic carbon source after impurities have been removed is 20:(0.5-2).

[0013] Preferably, the anthracite is selected from No. 3 anthracite;

[0014] The organic carbon source is selected from one or more of pitch, phenolic resin and cellulose;

[0015] And / or, the protective atmosphere is selected from one or more of argon, helium, neon, krypton, xenon and radon;

[0016] And / or, the hydrocarbon gas is selected from one or more of methane, acetylene, ethylene, propane and natural gas.

[0017] Preferably, the pyrolysis temperature in step S2) is 400℃~500℃; the pyrolysis time is 1~3h; and the pyrolysis heating rate is 1~10℃ / min.

[0018] Preferably, the carbon coating temperature in step S3) is 400℃~500℃; the carbon coating time is 1~3h; and the heating rate of the carbon coating is 3~7℃ / min.

[0019] Preferably, the volume ratio of the protective atmosphere to the hydrocarbon gas is 5:(0.5-2); the flow rate of the hydrocarbon gas is 150-250 mL / min.

[0020] Preferably, the high-temperature carbonization temperature in step S4) is 1000℃~1500℃; the high-temperature carbonization time is 1~3h; and the high-temperature carbonization heating rate is 1~10℃ / min.

[0021] The present invention also provides a negative electrode material for sodium-ion batteries, comprising carbon materials prepared by the above preparation method.

[0022] The present invention also provides a sodium-ion battery, comprising the above-described negative electrode material for sodium-ion batteries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) This invention uses a two-stage carbonization process to prepare coal-based hard carbon. Anthracite is used as a precursor. Different carbon sources are introduced to coat the anthracite with carbon. Then, after a carbon deposition process, the carbon anode material is obtained by high-temperature carbonization.

[0025] 2) The preparation method of the present invention requires few raw materials and reagents, the synthesis process conditions are easy to control, the operation is simple, the temperature is low, the energy consumption is low, the yield is high, and it is easy to industrialize. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the carbon material obtained in Example 1 of the present invention;

[0027] Figure 2 The image shows the XRD pattern of the carbon material obtained in Example 1 of this invention.

[0028] Figure 3 This is a graph showing the cycling performance of the carbon material obtained in Example 1 of the present invention;

[0029] Figure 4 This is a graph showing the cycling performance of the carbon material obtained in Example 2 of the present invention;

[0030] Figure 5 This is a graph showing the cycling performance of the carbon material obtained in Example 3 of the present invention;

[0031] Figure 6 This is a graph showing the cycling performance of the carbon material obtained in Example 4 of the present invention;

[0032] Figure 7 This is a graph showing the cycling performance of the carbon material obtained in Comparative Example 1 of the present invention;

[0033] Figure 8 This is a graph showing the cycling performance of the carbon material obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] This invention provides a method for preparing carbon materials, comprising the following steps: S1) removing impurities from anthracite coal to obtain anthracite coal with impurities removed; S2) grinding the anthracite coal with impurities removed to obtain ground anthracite coal; S3) passing a hydrocarbon gas through the ground anthracite coal in a protective atmosphere to perform carbon coating by chemical vapor deposition to obtain carbon-coated coal powder; S4) carbonizing the carbon-coated coal powder at high temperature in a protective atmosphere to obtain carbon materials.

[0036] In this invention, there are no special restrictions on the source of any of the raw materials.

[0037] Anthracite is subjected to impurity removal treatment to obtain anthracite with impurities removed; the anthracite can be any anthracite known to those skilled in the art, and there are no special restrictions, but No. 3 anthracite is preferred in this invention; the impurity removal treatment can be carried out by methods known to those skilled in the art, and there are no special restrictions, but in this invention, the impurity removal treatment is preferably carried out using a mixed solution of hydrochloric acid and hydrofluoric acid; the concentration of hydrochloric acid in the mixed solution of hydrochloric acid and hydrofluoric acid is preferably 3-6 mol / L, more preferably 4-5 mol / L; the mass concentration of hydrofluoric acid in the mixed solution of hydrochloric acid and hydrofluoric acid is preferably 5%-15%, more preferably 8%-12%, and even more preferably 10%; after the impurity removal treatment, it is preferred to wash repeatedly with deionized water to obtain anthracite with impurities removed.

[0038] In a specific embodiment of the present invention, the anthracite coal after impurities have been removed is ground to obtain ground anthracite coal; the grinding method is preferably ball milling; the grinding time is preferably 10-30 hours, more preferably 15-25 hours, and even more preferably 20 hours; the particle size of the ground anthracite coal is preferably less than or equal to 500 mesh.

[0039] In another specific embodiment of the present invention, an organic carbon source is added during grinding, followed by pyrolysis to obtain ground anthracite; the mass ratio of the anthracite with impurities removed to the organic carbon source is preferably 20:(0.5-2), more preferably 20:(0.5-1.5), even more preferably 20:(0.8-1.2), and most preferably 20:1; the organic carbon source can be any organic carbon source well known to those skilled in the art, and there are no special limitations. In the present invention, it is preferably one or more of asphalt, phenolic resin, and cellulose; the asphalt is preferably coal tar pitch. The grinding method is preferably ball milling; the grinding time is preferably 10-30 h, more preferably 15-25 h, and even more preferably 20 h; the anthracite coal with impurities removed is ground with the organic carbon source to a particle size preferably less than or equal to 500 mesh; the pyrolysis temperature is preferably 400℃-500℃, more preferably 420℃-480℃, even more preferably 440℃-460℃, and most preferably 450℃; the pyrolysis time is preferably 1-3 h, more preferably 1.5-2.5 h, and even more preferably 2 h; the pyrolysis heating rate is preferably 1-10℃ / min.

[0040] The ground anthracite is carbonized by chemical vapor deposition (CVD) after passing a hydrocarbon gas through a protective atmosphere to obtain carbon-coated coal powder. The protective atmosphere can be any atmosphere known to those skilled in the art and is not particularly limited. In this invention, one or more of argon, helium, neon, krypton, xenon, and radon are preferred. The hydrocarbon gas is preferably one or more of methane, acetylene, ethylene, propane, and natural gas. The volume ratio of the protective atmosphere to the hydrocarbon gas is preferably 5:(0.5-2). The flow rate of the hydrocarbon gas is preferably 150-250 mL / min, more preferably 180-220 mL / min, and even more preferably 200 mL / min; the carbon coating temperature is preferably 400℃-500℃, more preferably 420℃-480℃, even more preferably 440℃-460℃, and most preferably 450℃; the carbon coating time is preferably 1-3 h, more preferably 1.5-2.5 h, and even more preferably 2 h; the heating rate of the carbon coating is preferably 3-7℃ / min.

[0041] The carbon-coated coal powder is carbonized at high temperature in a protective atmosphere to obtain carbon material. The protective atmosphere can be any atmosphere known to those skilled in the art and is not particularly limited. In this invention, it is preferably one or more of argon, helium, neon, krypton, xenon, and radon. The high-temperature carbonization temperature is preferably 1000℃~1500℃, more preferably 1200℃~1500℃, even more preferably 1200℃~1400℃, and most preferably 1300℃. The high-temperature carbonization time (i.e., the holding time) is preferably 1~3h, more preferably 1.5~2.5h, and even more preferably 2h. The heating rate of the high-temperature carbonization is preferably 1~10℃ / min.

[0042] The present invention also provides a carbon material prepared by the above preparation method.

[0043] The present invention also provides a negative electrode material for sodium-ion batteries, comprising carbon materials prepared by the above preparation method.

[0044] The present invention also provides a sodium-ion battery, comprising the above-described negative electrode material for sodium-ion batteries.

[0045] More specifically, the sodium-ion battery includes a negative electrode, which includes a negative electrode active layer; the negative electrode active layer includes the aforementioned negative electrode material for sodium-ion batteries, a conductive agent, and a binder; the mass of the negative electrode material for sodium-ion batteries is preferably 80% to 95% of the negative electrode active mass, more preferably 80% to 90%, and even more preferably 80% to 85%.

[0046] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a carbon anode material and its preparation method, and a sodium-ion battery provided by the present invention.

[0047] All reagents used in the following examples are commercially available; the anthracite used in the examples is No. 3 anthracite; the pitch is coal tar pitch; the commercial glass fiber used in the examples is GF / B GMF Circles.

[0048] Example 1

[0049] Step 1: Wash the anthracite with a mixed acid solution (5 mol / L hydrochloric acid, 10 wt.% hydrofluoric acid) to remove impurities, and then wash repeatedly with deionized water to obtain anthracite with impurities removed.

[0050] Step 2: Add the anthracite coal and pitch, which have been de-impaired, to a ball mill at a mass ratio of 20:1 and ball mill for 20 hours to obtain a pitch-coated coal powder with a particle size of 500 mesh.

[0051] Step 3: Pre-carbonize the ball-milled pitch-coated coal powder from Step 2 at 450℃ for 2 hours to obtain coated pyrolysis coal powder.

[0052] Step 4: Place the coated pyrolytic coal powder from Step 3 under an acetylene atmosphere at a flow rate of 200 mL / min. -1 Carbon deposition was carried out at 450℃ for 2 hours to obtain deposited coal powder.

[0053] Step 5: The deposited coal powder obtained in Step 4 is subjected to high-temperature carbonization in an argon atmosphere. The carbonization temperature is 1300℃ and the carbonization time is 2h to obtain carbon material with a yield of 89%.

[0054] The carbon material obtained in Example 1 was analyzed using a scanning electron microscope, and its scanning electron microscope image is shown below. Figure 1 As shown, a is the SEM image of the carbon material at 1K magnification, b is the SEM image of the carbon material at 3K magnification, and c is the SEM image of the carbon material at 5K magnification.

[0055] The carbon material obtained in Example 1 was analyzed using X-ray diffraction, and its XRD pattern is shown below. Figure 2 As shown.

[0056] The carbon material was thoroughly and uniformly mixed with the conductive agent Super P and CMC (80:10:10). The slurry was then uniformly coated onto aluminum foil (1.3 mg / cm²). 2The cells were weighed and assembled in a glove box using a sodium metal sheet as the counter electrode and commercial glass fiber as the separator. A 1 mol / L electrolyte (solute NaClO4, solvent V(EC):V(EMC):V(DMC) volume ratio = 1:1:1) was used. The battery assembly sequence was: positive electrode shell → electrode sheet → electrolyte → separator → electrolyte → sodium sheet → current collector → spring sheet → negative electrode shell. The battery was then sealed using a sealing machine. Finally, it was allowed to stand at room temperature for 12 hours to test its electrochemical performance. The cycle performance graph is shown below. Figure 3 As shown, when charged and discharged at a rate of 0.1C between 0.005 and 3V, its initial coulombic efficiency reaches 84%, the initial discharge capacity is 304 mAh / g, and the capacity retention rate is 76.3% after 50 cycles.

[0057] Example 2

[0058] Step 1: Wash the anthracite with 5 mol / L hydrochloric acid and 10 wt.% hydrofluoric acid to remove impurities, and then wash repeatedly with deionized water to obtain anthracite with impurities removed.

[0059] Step 2: Add the smokeless coal (after removing impurities) and phenolic resin to a ball mill at a mass ratio of 20:1 and ball mill for 20 hours to obtain phenolic resin-coated coal powder with a particle size of 500 mesh.

[0060] Step 3: Pre-carbonize the phenolic resin-coated coal powder from Step 2 at 450℃ for 2 hours to obtain coated pyrolysis coal powder.

[0061] Step 4: Place the coated pyrolytic coal powder from Step 3 under an acetylene atmosphere at a flow rate of 200 mL / min. -1 Carbon deposition was carried out at 450℃ for 2 hours to obtain deposited coal powder.

[0062] Step 5: The deposited coal powder obtained in Step 4 is subjected to high-temperature carbonization in an argon atmosphere. The carbonization temperature is 1300℃ and the carbonization time is 2h to obtain carbon material with a yield of 83%.

[0063] The carbon material was thoroughly and uniformly mixed with the conductive agent Super P and CMC (80:10:10). The slurry was then uniformly coated onto aluminum foil (1.3 mg / cm²). 2The cells were weighed and assembled in a glove box using a sodium metal sheet as the counter electrode and commercial glass fiber as the separator. A 1 mol / L electrolyte (solute NaClO4, solvent V(EC):V(EMC):V(DMC) volume ratio = 1:1:1) was used. The battery assembly sequence was: positive electrode shell → electrode sheet → electrolyte → separator → electrolyte → sodium sheet → current collector → spring sheet → negative electrode shell. The battery was then sealed using a sealing machine. Finally, it was allowed to stand at room temperature for 12 hours to test its electrochemical performance. The cycle performance graph is shown below. Figure 4 As shown, when charged and discharged at a rate of 0.1C between 0.005 and 3V, its initial coulombic efficiency reaches 80%, the initial discharge capacity is 340mAh / g, and the capacity retention rate is 74% after 50 cycles.

[0064] Example 3

[0065] Step 1: Wash the anthracite with 5 mol / L hydrochloric acid and 10 wt.% hydrofluoric acid to remove impurities, and then wash repeatedly with deionized water to obtain anthracite with impurities removed.

[0066] Step 2: Add the anthracite coal (after removing impurities) and cellulose to a ball mill at a mass ratio of 20:1 and ball mill for 20 hours to obtain cellulose-coated coal powder with a particle size of 500 mesh.

[0067] Step 3: Pre-carbonize the ball-milled cellulose-coated coal powder from Step 2 at 450℃ for 2 hours to obtain coated pyrolysis coal powder.

[0068] Step 4: Place the coated pyrolytic coal powder from Step 3 under an acetylene atmosphere at a flow rate of 200 mL / min. -1 Carbon deposition was carried out at 450℃ for 2 hours to obtain deposited coal powder.

[0069] Step 5: The deposited coal powder obtained in Step 4 is subjected to high-temperature carbonization in an argon atmosphere. The carbonization temperature is 1300℃ and the carbonization time is 2h to obtain carbon material with a yield of 88%.

[0070] The carbon material was thoroughly and uniformly mixed with the conductive agent Super P and CMC (80:10:10). The slurry was then uniformly coated onto aluminum foil (1.3 mg / cm²). 2The cells were weighed and assembled in a glove box using a sodium metal sheet as the counter electrode and commercial glass fiber as the separator. A 1 mol / L electrolyte (solute NaClO4, solvent V(EC):V(EMC):V(DMC) volume ratio = 1:1:1) was used. The battery assembly sequence was: positive electrode shell → electrode sheet → electrolyte → separator → electrolyte → sodium sheet → current collector → spring sheet → negative electrode shell. The battery was then sealed using a sealing machine. Finally, it was allowed to stand at room temperature for 12 hours to test its electrochemical performance. The cycle performance graph is shown below. Figure 5 As shown, when charged and discharged at a rate of 0.1C between 0.005 and 3V, its initial coulombic efficiency reaches 86%, the initial discharge capacity is 325mAh / g, and the capacity retention rate is 72% after 50 cycles.

[0071] As can be seen from Examples 1-3, coating anthracite can reduce surface defects and thus improve the first coulombic efficiency of hard carbon in anthracite.

[0072] Example 4

[0073] Step 1: Wash the anthracite with a mixed acid solution (5 mol / L hydrochloric acid, 10 wt.% hydrofluoric acid) to remove impurities, and then wash repeatedly with deionized water to obtain anthracite with impurities removed.

[0074] Step 2: Add the anthracite obtained in Step 1 (after removing impurities) to a ball mill and ball mill for 20 hours to obtain ball-milled coal powder with a particle size of 500 mesh.

[0075] Step 3: The ball-milled coal powder from Step 2 is subjected to an acetylene atmosphere at a flow rate of 200 mL / min. -1 Carbon deposition was performed at 450℃ for 2 hours.

[0076] Step 4: The acetylene carbon-coated coal powder prepared in Step 3 is subjected to high-temperature carbonization under an argon atmosphere. The carbonization temperature is 1300℃ and the carbonization time is 2h to obtain carbon material with a yield of 89%.

[0077] The carbon material was thoroughly and uniformly mixed with the conductive agent Super P and CMC (80:10:10). The slurry was then uniformly coated onto aluminum foil (1.3 mg / cm²). 2The cells were weighed and assembled in a glove box using a sodium metal sheet as the counter electrode and commercial glass fiber as the separator. A 1 mol / L electrolyte (solute NaClO4, solvent V(EC):V(EMC):V(DMC) volume ratio = 1:1:1) was used. The battery assembly sequence was: positive electrode shell → electrode sheet → electrolyte → separator → electrolyte → sodium sheet → current collector → spring sheet → negative electrode shell. The battery was then sealed using a sealing machine. Finally, it was allowed to stand at room temperature for 12 hours to test its electrochemical performance. The cycle performance graph is shown below. Figure 6 As shown. Charge-discharge cycles were performed at a rate of 0.1C between 0.005 and 3V.

[0078] Example 5

[0079] The hard carbon material was prepared according to the conditions of Example 3, except that different carbon hydrocarbon atmospheres were used to prepare the material. The performance of anthracite carbon material prepared by carbon deposition in different carbon hydrocarbon atmospheres in sodium-ion batteries was investigated, and the results are shown in Table 1.

[0080] Table 1. Performance comparison of anthracite carbon materials prepared by carbon deposition in different hydrocarbon atmospheres in sodium-ion batteries.

[0081]

[0082] Different carbon coating methods significantly alter the performance of anthracite hard carbon. Anthracite hard carbon coated with pitch, phenolic resin, and cellulose exhibits high capacity, but cellulose-coated anthracite shows superior electrochemical performance after acetylene deposition. Carbon hydrocarbon gases decompose at high temperatures, generating carbon free radicals. These free radicals gradually deposit on the anthracite surface. During anthracite pyrolysis, small-molecule gases volatilize, creating numerous voids and defects. These carbon free radicals deposit in these voids, controlling the specific surface area and reducing surface defects. Therefore, using carbon hydrocarbon gases can greatly improve the initial coulombic efficiency of anthracite hard carbon. However, the carbon free radicals generated by the cracking of different hydrocarbons vary considerably. Hydrocarbons with larger molecular weights produce larger deposited carbon particles, which are less effective at filling voids on the anthracite surface and thus less effective at coating anthracite hard carbon. Overall, acetylene is the most effective carbon source for coating.

[0083] Comparative Example 1

[0084] Step 1: Wash the anthracite with 5 mol / L hydrochloric acid and 10 wt.% hydrofluoric acid to remove impurities, and then wash repeatedly with deionized water to obtain anthracite with impurities removed.

[0085] Step 2: Add the anthracite coal (after removing impurities) from Step 1) into a ball mill and ball mill for 20 hours to obtain pulverized coal with a particle size of 500 mesh.

[0086] In step 3, the coal powder prepared in step 2 was subjected to high-temperature carbonization under an argon atmosphere at a carbonization temperature of 1300℃ for 2 hours to obtain carbon material with a yield of 71%.

[0087] The carbon material was thoroughly and uniformly mixed with the conductive agent Super P and CMC (80:10:10). The slurry was then uniformly coated onto aluminum foil (1.3 mg / cm²). 2 The cells were weighed and assembled in a glove box using a sodium metal sheet as the counter electrode and commercial glass fiber as the separator. A 1 mol / L electrolyte (solute NaClO4, solvent V(EC):V(EMC):V(DMC) volume ratio = 1:1:1) was used. The battery assembly sequence was: positive electrode shell → electrode sheet → electrolyte → separator → electrolyte → sodium sheet → current collector → spring sheet → negative electrode shell. The battery was then sealed using a sealing machine. Finally, it was allowed to stand at room temperature for 12 hours to test its electrochemical performance. The cycle performance graph is shown below. Figure 7 As shown. When charged and discharged at a rate of 0.1C between 0.005 and 3V, the initial coulombic efficiency reached 72%, the initial discharge capacity was 250 mAh / g, and the capacity retention after 50 cycles was 50%.

[0088] Comparative Example 2

[0089] Step 1: Wash the anthracite with 5 mol / L hydrochloric acid and 10 wt.% hydrofluoric acid to remove impurities, and then wash repeatedly with deionized water to obtain anthracite with impurities removed.

[0090] Step 2: Add the anthracite coal (after removing impurities) and cellulose from Step 1 to a ball mill at a mass ratio of 20:1 and ball mill for 20 hours to obtain cellulose-coated coal powder with a particle size of 500 mesh.

[0091] Step 3: Pre-carbonize the ball-milled cellulose-coated coal powder from Step 2 at 450℃ for 2 hours to obtain coated pyrolysis coal powder.

[0092] Step 4: The coated pyrolytic coal powder from Step 3 is subjected to high-temperature carbonization under an argon atmosphere. The carbonization temperature is 1300℃ and the carbonization time is 2h to obtain carbon material with a yield of 85%.

[0093] The carbon material was thoroughly and uniformly mixed with the conductive agent Super P and CMC (80:10:10). The slurry was then uniformly coated onto aluminum foil (1.3 mg / cm²). 2The cells were weighed and assembled in a glove box using a sodium metal sheet as the counter electrode and commercial glass fiber as the separator. A 1 mol / L electrolyte (solute NaClO4, solvent V(EC):V(EMC):V(DMC) volume ratio = 1:1:1) was used. The battery assembly sequence was: positive electrode shell → electrode sheet → electrolyte → separator → electrolyte → sodium sheet → current collector → spring sheet → negative electrode shell. The battery was then sealed using a sealing machine. Finally, it was allowed to stand at room temperature for 12 hours to test its electrochemical performance. The cycle performance graph is shown below. Figure 8 As shown. Charge-discharge cycling at a rate of 0.1C between 0.005 and 3V yielded an initial coulombic efficiency of 72%, an initial discharge capacity of 250 mAh / g, and a capacity retention of 50% after 50 cycles.

[0094] As can be seen from Comparative Examples 1 and 2, directly carbonized anthracite has more surface defects, a large number of macropores, and a low residual carbon rate, indicating that the volatile matter content is relatively high. This results in a low initial coulombic efficiency and low capacity of sodium-ion batteries, which cannot meet the practical application requirements of sodium-ion batteries.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for producing a carbon material, characterized by, The method comprises the following steps: S1) removing impurities from anthracite to obtain anthracite with impurities removed; S2) grinding the anthracite with impurities removed to obtain ground anthracite; S3) carbon-coating the ground anthracite in a protective atmosphere by introducing a carbon hydrocarbon gas to obtain carbon-coated coal powder; S4) high-temperature carbonizing the carbon-coated coal powder in a protective atmosphere to obtain carbon material; The organic carbon source is added during grinding in step S2), and then pyrolysis is performed to obtain the ground anthracite; The mass ratio of the anthracite with impurities removed to the organic carbon source is 20:(0.5-2); The organic carbon source is selected from one or more of pitch, phenolic resin, and cellulose.

2. The production method according to claim 1, characterized by, The anthracite is selected from No. 3 anthracite; The protective atmosphere is selected from one or more of argon, helium, neon, krypton, xenon, and radon; The carbon hydrocarbon gas is selected from one or more of methane, acetylene, ethylene, propane, and natural gas.

3. The preparation method according to claim 1, characterized in that, The pyrolysis temperature in step S2) is 400-500 DEG C; the pyrolysis time is 1-3 h; and the pyrolysis heating rate is 1-10 DEG C / min.

4. The method of claim 1, wherein, The carbon-coating temperature in step S3) is 400-500 DEG C; the carbon-coating time is 1-3 h; and the carbon-coating heating rate is 3-7 DEG C / min.

5. The preparation method according to claim 1, characterized in that, The volume ratio of the protective atmosphere to the carbon hydrocarbon gas is 5:(0.5-2); and the flow rate of the carbon hydrocarbon gas is 150-250 mL / min.

6. The method of claim 1, wherein, The high-temperature carbonization temperature in step S4) is 1000-1500 DEG C; the high-temperature carbonization time is 1-3 h; and the high-temperature carbonization heating rate is 1-10 DEG C / min.

7. A negative electrode material for a sodium-ion battery, characterized by, The carbon material prepared by the preparation method of any one of claims 1-6.

8. A sodium-ion battery, characterized in that, The negative electrode material for sodium ion batteries of claim 7.

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