Preparation of hard carbon with fast charging performance and application thereof in sodium battery

Abstract

The application relates to a preparation method of a hard carbon negative material with fast charging performance, which comprises the following steps: (S1) mixing a metal chloride salt with a thermoplastic precursor, heating and keeping warm in an oxygen-containing atmosphere to obtain a pretreated thermoplastic precursor; carrying out curing treatment on the thermosetting precursor and an acidic curing agent to obtain a pretreated thermosetting precursor; (S2) uniformly mixing the pretreated thermoplastic precursor and the pretreated thermosetting precursor, pre-carbonizing in an inert atmosphere; and high-temperature carbonizing in an inert atmosphere or a carbon-hydrogen gas atmosphere to obtain a hard carbon material; the pretreated thermosetting precursor accounts for 50-90% of the total mass of the pretreated thermosetting precursor and the pretreated thermoplastic precursor. According to the method, the hard carbon material with a large number of small-aperture closed pores is prepared by mixing the thermosetting and thermoplastic precursors in different proportions, the hard carbon material has high capacity and high rate performance, and the hard carbon material also exhibits excellent cycle stability in a fast-charging sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of battery anode material technology, specifically relating to a method for preparing hard carbon with fast-charging performance as a sodium-ion battery anode material. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in portable electronic products and electric vehicles due to their long lifespan and high energy density. However, with the widespread use of lithium-ion batteries and the scarcity and uneven distribution of lithium resources, the price of lithium has continued to rise, making it difficult to meet the growing demand of the electric vehicle market. Furthermore, the insufficient power density of lithium-ion batteries leads to excessively long charging times, causing "charging anxiety." In particular, graphite anodes are prone to lithium plating during fast charging, accelerating battery degradation and potentially posing safety hazards. In contrast, sodium resources are abundant, widely distributed, and relatively inexpensive, making them a strong complement to lithium-ion batteries. Due to thermodynamic limitations, commercially available graphite anode materials cannot effectively intercalate sodium ions, thus graphite as a sodium-ion battery anode material exhibits almost no sodium storage activity. Therefore, developing novel high-capacity, low-cost anode materials is crucial for the commercialization of sodium-ion batteries.

[0003] Currently, common sodium-ion battery anode materials include carbon-based materials, titanium-based materials, organic materials, and alloy materials. Among them, hard carbon materials are considered the most mature and commercially viable sodium-ion battery anode materials due to their low operating voltage (<0.1V), low cost, and simple preparation. However, the sodium storage process of hard carbon below 0.05V is extremely slow, resulting in poor rate performance (capacity drop of up to 60% at 1C current density), making it difficult to meet market demand for fast-charging sodium-ion batteries. Therefore, designing and fabricating hard carbon materials that maintain a long plateau capacity at high current densities is of great significance for realizing fast-charging sodium-ion batteries.

[0004] CN103094528A discloses a hard carbon anode material for lithium-ion power and energy storage batteries. Its preparation method includes the following steps: using the pyrolysis product of a thermosetting resin or a mixture of thermosetting and thermoplastic resins as a hard carbon matrix, and using carbon material as a coating to obtain the hard carbon anode material. CN116425140A discloses a nitrogen-doped hard carbon material and its preparation method, including the following steps: 1) mixing phenolic resin and melamine resin, and then preparing a carbon source precursor under the action of a curing agent or curing agent additive; 2) heating the prepared carbon source precursor to 600-800℃ at 5-10℃ / min, and then further heating it to 1200-1400℃ at 0.5-5℃ / min to complete carbonization, thereby obtaining the nitrogen-doped hard carbon material. CN116022769A discloses a method for preparing a hard carbon anode material for sodium-ion batteries, comprising the following steps: (1) mixing a resin precursor and an alcohol solvent, adding zinc oxide, and obtaining a hard carbon precursor after stirring and curing; (2) subjecting the hard carbon precursor obtained in step (1) to carbonization treatment under an inert atmosphere, and obtaining the hard carbon anode material for sodium-ion batteries after crushing, acid washing and sieving. The resin precursor includes any one or a combination of at least two of phenolic resin precursor, furan resin precursor or furfural resin precursor, preferably a phenolic resin precursor; preferably, the phenolic resin includes thermoplastic phenolic resin and / or thermosetting phenolic resin.

[0005] Existing technologies have reported the use of thermosetting and thermoplastic resins as precursors to prepare hard carbon materials. However, this involves a simple physical mixing of thermosetting and thermoplastic precursors, which cannot achieve molecular-level interconnection. Ultimately, this can only increase the sodium storage capacity of hard carbon, but cannot modify it at the molecular level to improve its rate performance. Summary of the Invention

[0006] To overcome the shortcomings of insufficient rate performance in existing hard carbon anode materials, this invention proposes a method for preparing hard carbon with a specific microstructure. This invention pretreats thermoplastic and thermosetting precursors using different methods, increasing the functional groups in each. During the pre-carbonization process after mixing, the macromolecular chains in the pretreated thermoplastic and thermosetting precursors undergo bonding reactions, affecting the degree of crosslinking of the precursors. This results in a hard carbon material with a pore size less than 1.7 nm and a pore size factor greater than 0.03 after carbonization. By mixing thermosetting and thermoplastic precursors in different proportions, the degree of crosslinking of the carbon layer during calcination is altered, obtaining a hard carbon material with a pore size less than 1.7 nm and a pore size factor greater than 0.03, thereby improving its rate performance and ultimately enabling the assembly of full batteries to enhance the fast-charging performance of sodium-ion batteries.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a fast-charging performance hard carbon anode material includes the following steps:

[0009] (S1) Metal chloride salts are mixed with thermoplastic precursors and heated and kept at a temperature in an oxygen-containing atmosphere to obtain pretreated thermoplastic precursors; thermosetting precursors and acidic curing agents are cured to obtain pretreated thermosetting precursors.

[0010] (S2) Mix the pretreated thermoplastic precursor and the pretreated thermosetting precursor evenly, and pre-carbonize them in an inert atmosphere; then carbonize them at high temperature in an inert atmosphere or a hydrocarbon gas atmosphere to obtain hard carbon material; the pretreated thermosetting precursor accounts for 50-90% of the total mass of the pretreated thermosetting precursor and the pretreated thermoplastic precursor.

[0011] Further, in step (S1), the thermoplastic precursor is selected from at least one of polyvinyl chloride, polyaniline, asphalt, coal, and petroleum coke; the metal salt chlorination is selected from at least one of NaCl, KCl, ZnCl2, MgCl2, and CaCl2; the mass ratio of thermoplastic precursor to metal salt chlorination is 1:0.5-1. The metal chloride catalyzes the polymerization of the precursor at high temperatures and promotes the formation of carboxyl and carbonyl functional groups.

[0012] Further, in step (S1), the thermosetting precursor is selected from at least one of phenolic resin, epoxy resin, sucrose, cellulose, and cotton; the acidic curing agent is selected from at least one of oxalic acid, phosphoric acid, benzenesulfonic acid, tartaric acid, citric acid, and anhydrous benzoic acid. The mass ratio of the thermosetting precursor to the acidic curing agent is 1:0.1-0.3. The acidic curing agent increases the crosslinking degree of the precursor during the curing process and catalyzes the generation of hydroxyl functional groups.

[0013] Furthermore, in step (S1), the oxygen-containing atmosphere refers to an oxygen content greater than 20%, such as air, oxygen, or a mixture of air and oxygen; the heating and holding temperature is increased to 200-300℃ at a heating rate of 2-10℃ / min, and held for 5-10 hours.

[0014] Further, in step (S2), the pretreated thermosetting precursor accounts for 60-80% of the total mass of the pretreated thermosetting precursor and the pretreated thermoplastic precursor; preferably, the pretreated thermosetting precursor accounts for 70-80% of the total mass of the pretreated thermosetting precursor and the pretreated thermoplastic precursor.

[0015] More preferably, the thermosetting precursor is phenolic resin and epoxy resin, and the thermoplastic precursor is asphalt. This can yield a hard carbon anode material with optimal specific capacity and rate performance. The possible reason is that the thermoplastic precursor with a low degree of crosslinking reacts with the thermosetting precursor with a high degree of crosslinking when mixed, which not only reduces the overall degree of crosslinking, but also generates a rich closed-cell structure in the subsequent carbonization process.

[0016] Furthermore, in step (S2), the method of uniform mixing is not particularly limited, including but not limited to ball milling, grinding, sand milling, etc. Ball milling is preferred, with a ball-to-material ratio of 10-20:1, a rotation speed of 400-700 rpm, and a ball milling time of 3-10 hours.

[0017] Further, in step (S2), the pre-carbonization is carried out under an inert atmosphere by heating to 500-800℃ and holding for 2-5 hours, wherein the inert atmosphere is an argon atmosphere and the heating rate is 1-3℃ / min; the inert atmosphere is at least one of nitrogen and argon.

[0018] Further, in step (S2), the high-temperature carbonization is carried out by heating to 1000-1700℃, preferably 1300-1500℃, at a heating rate of 5-10℃ / min, and then holding the temperature for calcination for 5-10 hours.

[0019] Slow heating rates during pre-carbonization are beneficial for forming a uniform and disordered cross-linked structure. Conversely, if the heating rate is too fast, the cross-linking copolymerization will be insufficient, which will cause the local polymer carbon to undergo direct condensation into mesophase carbon microspheres with sheet-like ordered polymers. Subsequent high-temperature calcination will generate long-range ordered and tightly stacked graphene layers, which is not conducive to the storage of sodium ions and is detrimental to improving the material's capacity.

[0020] Furthermore, in step (S2), after the high-temperature carbonization is completed, there is an acid washing step, in which the carbonized material is mixed and stirred in an inorganic acid for 10-24 hours, washed, and dried to obtain the hard carbon anode material of the present invention. The purpose of acid washing is to remove impurities.

[0021] The present invention also provides a sodium-ion battery anode material, comprising hard carbon material, conductive additives, and binder, wherein the hard carbon material is prepared by the above-described preparation method.

[0022] The superior effect of this invention lies in providing a method for preparing and applying an organic polymer-based sodium-ion battery anode material. This invention uses inexpensive and technologically mature industrial organic polymers as raw materials. Pre-oxidation increases the crosslinking degree of the precursor, followed by mixing the pre-oxidized thermosetting and thermoplastic precursors, significantly improving the specific capacity and rate performance of the hard carbon material. This invention's preparation method is low-cost, simple, and has a high carbon yield, making it suitable for large-scale production of hard carbon materials, which are then applied as anode materials in sodium-ion secondary batteries. The reaction between the thermoplastic precursor with a lower degree of crosslinking and the thermosetting precursor with a higher degree of crosslinking during mixing not only reduces the overall crosslinking degree but also generates abundant closed-cell structures during subsequent carbonization. Therefore, the resulting hard carbon material, when used in sodium-ion batteries, exhibits excellent rate performance while also maintaining a plateau capacity. Attached Figure Description

[0023] Figure 1 This is a TEM image of the hard carbon material prepared in Example 1.

[0024] Figure 2 This is a TEM image of the hard carbon material prepared in Example 2.

[0025] Figure 3 This is a TEM image of the hard carbon material prepared in Example 3.

[0026] Figure 4 This is a TEM image of the hard carbon material prepared in Example 4.

[0027] Figure 5 This is a TEM image of the hard carbon material prepared in Example 5.

[0028] Figure 6 This is the small-angle X-ray scattering spectrum of the hard carbon material prepared in Example 3.

[0029] Figure 7 This is the small-angle X-ray scattering spectrum of the hard carbon material prepared in Example 6. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. The following embodiments are provided to better understand this invention, but do not limit the invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods.

[0031] Example 1

[0032] (S1) Phenolic resin and oxalic acid in a mass ratio of 1:0.2 are dissolved in ethanol, heated and stirred on a heating platform at 80°C for 8 hours. After cooling, the solidified particles are obtained as the pretreated thermosetting precursor.

[0033] (S2) After grinding and mixing asphalt and ZnCl2 at a mass ratio of 1:0.5, the mixture is placed in a muffle furnace and heated in air at a heating rate of 5℃ / min, a heating temperature of 300℃, and a holding time of 8 hours. After cooling, a pretreated thermoplastic precursor is obtained.

[0034] (S3) Grind the pretreated particles in steps (1) and (2) into powder, weigh 90 parts by mass of the pretreated thermosetting precursor and 10 parts by mass of the pretreated thermoplastic precursor and place them in a ball mill jar, control the ball-to-material ratio to be 20:1, set the ball mill speed to 450 rpm, and use forward and reverse rotation mode to ball mill for 4 hours to obtain the mixed precursor.

[0035] (S4) The mixed precursor was placed in a tube furnace and calcined at a heating rate of 3℃ / min. The temperature was raised to 600℃ and held for 2 hours in an Ar atmosphere to obtain a pre-carbonized precursor. The precursor was then ground and refined and sieved through a 200-mesh sieve.

[0036] (S5) The above mixed precursor is placed in a high-temperature tube furnace and calcined under an argon atmosphere at a heating rate of 10℃ / min. After heating to 1000℃, it is held for 7 hours and then cooled to room temperature to obtain the hard carbon anode material. The mixture is then calcined, cooled to room temperature, ground, and placed in a hydrochloric acid solution and stirred for 24 hours. After washing with deionized water and drying, the hard carbon anode material is obtained.

[0037] Example 2

[0038] The other conditions and operations are the same as in Example 1, except that in step (S5), the calcination temperature is changed from 1000℃ to 1300℃.

[0039] Example 3

[0040] The other conditions and operations are the same as in Example 1, except that in step (S5), the calcination temperature is changed from 1000℃ to 1500℃.

[0041] Example 4

[0042] The other conditions and operations are the same as in Example 1, except that in step (S5), the calcination temperature is changed from 1000℃ to 1700℃.

[0043] Example 5

[0044] The other conditions and operations are the same as in Example 1, except that in step (S5), the calcination temperature is changed from 1000℃ to 2000℃.

[0045] Figure 1 This is a TEM image of the hard carbon material prepared in Example 1; Figure 2 This is a TEM image of the hard carbon material prepared in Example 2; Figure 3 This is a TEM image of the hard carbon material prepared in Example 3; Figure 4 This is a TEM image of the hard carbon material prepared in Example 4; Figure 5 This is a TEM image of the hard carbon material prepared in Example 5. It can be seen that the hard carbon material obtained in Example 1 exhibits a turbine-like structure, but the overall pseudo-graphite domain length is relatively short, and no obvious closed-pore structure appears. When the carbonization temperature increases to 1300℃, the curved graphite domains in the hard carbon material obtained in Example 2 gradually lengthen and accumulate to form a closed-pore structure with a pore diameter of approximately 1.3 nm. As the carbonization temperature further increases, the diameter of the closed pores produced by the hard carbon materials in Examples 3, 4, and 5 continuously increases, and when the carbonization temperature reaches 2000℃, the diameter of the closed pores exceeds 5 nm.

[0046] Example 6

[0047] The other conditions and operations are the same as in Example 3, except that in step (S3), the thermosetting precursor is 80 parts by weight of pre-oxidized phenolic resin and the thermoplastic precursor is 20 parts by weight of pre-oxidized asphalt.

[0048] Example 7

[0049] The other conditions and operations are the same as in Example 3, except that in step (S3), the thermosetting precursor is 70 parts by weight of pre-oxidized phenolic resin and the thermoplastic precursor is 30 parts by weight of pre-oxidized asphalt.

[0050] Example 8

[0051] The other conditions and operations are the same as in Example 3, except that in step (S3), the thermosetting precursor is 60 parts by weight of pre-oxidized phenolic resin and the thermoplastic precursor is 40 parts by weight of pre-oxidized asphalt.

[0052] Example 9

[0053] The other conditions and operations are the same as in Example 3, except that in step (S3), the thermosetting precursor is 50 parts by weight of pre-oxidized phenolic resin and the thermoplastic precursor is 50 parts by weight of pre-oxidized asphalt.

[0054] Example 10

[0055] The other conditions and operations are the same as in Example 1, except that in step (S2), the asphalt is replaced by polyaniline, and the amount of pretreated thermosetting precursor is 80 parts by mass and the amount of pretreated thermoplastic precursor is 20 parts by mass.

[0056] Example 11

[0057] The other conditions and operations are the same as in Example 6, except that in step (S1), the phenolic resin is replaced by epoxy resin, and the amount of the pretreated thermosetting precursor is 80 parts by mass and the amount of the pretreated thermoplastic precursor is 20 parts by mass.

[0058] Comparative Example 1

[0059] (S1) Phenolic resin and oxalic acid in a mass ratio of 1:0.2 are dissolved in ethanol, heated and stirred on a heating platform at 80°C for 8 hours, and then cooled to obtain solidified particles.

[0060] (S2) The solidified particles are ground into powder and placed in a tube furnace for calcination at a heating rate of 3℃ / min. The temperature is raised to 600℃ and held for 2 hours in an Ar atmosphere to obtain a pre-carbonized precursor. The precursor is then ground and refined and sieved through a 200-mesh sieve.

[0061] (S3) The ground and sieved precursor is placed in a high-temperature tube furnace and calcined in an argon atmosphere at a heating rate of 10℃ / min. After heating to 1500℃, it is held for 7 hours and then cooled to room temperature to obtain the hard carbon anode material.

[0062] Comparative Example 2

[0063] (S1) After grinding and mixing asphalt and ZnCl2 at a mass ratio of 1:0.5, the mixture is placed in a muffle furnace and heated in air at a heating rate of 5℃ / min, a heating temperature of 300℃, and a holding time of 8 hours. After cooling, pre-oxidized particles are obtained.

[0064] (S2) The pre-oxidized particles were placed in a tube furnace and calcined at a heating rate of 3℃ / min. The temperature was raised to 600℃ and held for 2 hours in an Ar atmosphere to obtain a pre-carbonized precursor. The precursor was then ground and refined and sieved through a 200-mesh sieve.

[0065] (S5) The ground and sieved precursor is placed in a high-temperature tube furnace and calcined in an argon atmosphere at a heating rate of 10℃ / min. After heating to 1500℃, it is held for 7 hours and then cooled to room temperature to obtain the hard carbon anode material.

[0066] Comparative Example 3

[0067] The other conditions are the same as in Example 6, except that oxalic acid is not added in step (S1).

[0068] Comparative Example 4

[0069] The other conditions are the same as in Example 6, except that ZnCl2 is not added in step (S2).

[0070] Figure 6 This is the small-angle X-ray scattering pattern of Example 3. Figure 7This is the small-angle X-ray scattering pattern of Example 6; D and B in the figure are the average aperture and pore number factors obtained by fitting the small-angle X-ray scattering curve.

[0071] Application examples

[0072] Preparation and testing methods of negative electrode materials: The hard carbon negative electrode material, SuperP, and binder CMC / SBR obtained in the above examples and comparative examples were mixed at a mass ratio of 94:2:4. An appropriate amount of water was added to slurry the mixture, resulting in a uniformly mixed electrode slurry. The prepared electrode slurry was uniformly coated onto carbon-coated aluminum foil, dried, and then vacuum-dried at 60℃ for 12 hours before being sliced. Using a sodium metal sheet as the counter electrode, glass fiber as the separator, and 1 mol / L NaPF6 (solvent being ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) as the electrolyte, button batteries were assembled in an argon-protected glove box. Constant current charge-discharge tests were performed at a current density of 200 mA / g and a charge-discharge voltage range of 0.001-2.0 V. The test results are shown in Table 1.

[0073] Table 1 Electrochemical performance test of hard carbon anode materials

[0074]

[0075] from Figure 1 As can be seen, the hard carbon material prepared in Example 1 exhibits a cross-linked turbine-like structure. However, due to the low carbonization temperature and short carbon layer length, closed-cell structures are difficult to form in the cross-linked structure, thus failing to provide ideal conditions for the formation of quasi-metallic sodium. Figure 2 The results show that when the carbonization temperature is increased to 1300℃, the hard carbon material exhibits a clear graphite-like layer structure, and these layers are cross-linked to form a closed-cell structure. Figure 3 , Figure 4 and Figure 5 Further analysis shows that with increasing carbonization temperature, the length of the graphite-like domains increases significantly, leading to a continuous increase in the size of the closed pores, ultimately forming closed-pore structures with pore sizes as high as 5 nm when the carbonization temperature reaches 2000℃. These larger closed-pore structures facilitate the growth of quasi-sodium metal clusters. However, higher carbonization temperatures also result in narrower carbon interlayer spacing, reducing the diffusion rate of sodium ions; simultaneously, the growth of larger quasi-sodium metal clusters greatly restricts the sodium storage kinetics in the plateau region, which is detrimental to the rate performance of the material.

[0076] Figure 6 and Figure 7 Small-angle X-ray scattering spectra of Examples 3 and 6 are shown, and the correlation factor between the closed-pore diameter and the number of closed pores is calculated by fitting. The fitting formula is shown below:

[0077]

[0078] Where I is the scattering intensity as a function of Q; Q is the scattering amount; A is the surface scattering factor at low Q; B is the scale factor of pore scattering, which is proportional to the pore surface area; and a0 is a correlation factor with the pore size R, a0 = R × 10 -0.5 D is the background height.

[0079] from Figure 6 and Figure 7 It can be seen that when a small amount of thermoplastic precursor is added, the hard carbon material exhibits a larger closed-pore size, but a smaller number of closed pores. When the proportion of thermoplastic precursor is increased, the closed-pore size in the hard carbon material decreases from 3.11 nm to 1.69 nm, but the pore number correlation factor increases from 0.064 to 0.225. This indicates that the addition of thermoplastic precursor can slow down the increase in closed-pore size, thereby forming more small pores at higher carbonization temperatures. The formation of these small pores facilitates rapid sodium storage in the plateau region.

[0080] As shown in Table 1, the sodium storage capacity of hard carbon materials at 20 mA / g does not increase indefinitely with the increase of closed-pore size. On the contrary, the sodium storage capacity decreases after the closed-pore size increases to a certain extent. Furthermore, the rate performance of hard carbon materials also decreases with the increase of closed-pore size. For example, the hard carbon material prepared in Example 1 exhibits good rate performance, with a capacity retention rate of 75.7% at a current density of 200 mA / g, but its overall capacity is low due to the small number of pores. When the carbonization temperature is increased to 1500℃, the closed-pore size of the hard carbon material prepared in Example 3 increases to 3.1 nm, and the capacity increases to 346.8 mAh / g, but its rate performance is poor, with a capacity retention rate of only 33.8% at 200 mA / g. When the proportion of thermoplastic precursor is increased, the hard carbon material prepared in Example 6, although having a smaller closed-pore size, exhibits a larger number of pores, demonstrating a capacity of 400.4 mAh / g and a capacity retention rate of 88.4%.

Claims

1. A method for preparing a fast-charging performance hard carbon anode material, characterized in that, Includes the following steps: (S1) Metal chloride salts are mixed with thermoplastic precursors and heated and kept at a temperature in an oxygen-containing atmosphere to obtain pretreated thermoplastic precursors; thermosetting precursors and acidic curing agents are cured to obtain pretreated thermosetting precursors. Heating and heat preservation: Heat to 200-300℃ at a heating rate of 2-10℃ / min, and hold for 5-10 hours; (S2) Mix the pretreated thermoplastic precursor and the pretreated thermosetting precursor evenly, and pre-carbonize them in an inert atmosphere; then carbonize them at high temperature in an inert atmosphere or a hydrocarbon gas atmosphere to obtain hard carbon material; the pretreated thermosetting precursor accounts for 50-90% of the total mass of the pretreated thermosetting precursor and the pretreated thermoplastic precursor.

2. The preparation method according to claim 1, characterized in that, In step (S1), the thermoplastic precursor is selected from at least one of polyvinyl chloride, polyaniline, and asphalt; the metal salt chlorination is selected from at least one of NaCl, KCl, ZnCl2, MgCl2, and CaCl2.

3. The preparation method according to claim 2, characterized in that, In step (S1), the mass ratio of thermoplastic precursor to metal salt chlorination is 1:0.5-1.

4. The preparation method according to claim 1, characterized in that, In step (S1), the thermosetting precursor is selected from at least one of phenolic resin and epoxy resin; the acidic curing agent is selected from at least one of oxalic acid, phosphoric acid, tartaric acid and citric acid.

5. The preparation method according to claim 4, characterized in that, In step (S1), the mass ratio of the thermosetting precursor to the acid curing agent is 1:0.1-0.

3.

6. The preparation method according to claim 1, characterized in that, In step (S1), an oxygen-containing atmosphere refers to an oxygen content greater than 20%.

7. The preparation method according to claim 6, characterized in that, In step (S1), the oxygen-containing atmosphere is air, oxygen, or a mixture of air and oxygen.

8. The preparation method according to claim 1, characterized in that, In step (S2), the pretreated thermosetting precursor accounts for 60-80% of the total mass of the pretreated thermosetting precursor and the pretreated thermoplastic precursor.

9. The preparation method according to claim 1, characterized in that, In step (S2), the pretreated thermosetting precursor accounts for 70-80% of the total mass of the pretreated thermosetting precursor and the pretreated thermoplastic precursor.

10. The preparation method according to claim 1, characterized in that, The thermosetting precursor is phenolic resin and epoxy resin, and the thermoplastic precursor is asphalt.

11. The preparation method according to claim 1, characterized in that, In step (S2), the methods for achieving uniform mixing include ball milling, grinding, and sand milling.

12. The preparation method according to claim 1, characterized in that, In step (S2), the mixing method is ball milling, with a ball-to-material ratio of 10-20:1, a rotation speed of 400-700 rpm, and a ball milling time of 3-10 hours.

13. The preparation method according to claim 1, characterized in that, In step (S2), the pre-carbonization is carried out under an inert atmosphere by heating to 500-800℃ and holding for 2-5 hours. The inert atmosphere is an argon atmosphere, and the heating rate is 1-3℃ / min. The inert atmosphere is at least one of nitrogen and argon.

14. The preparation method according to claim 1, characterized in that, In step (S2), the high-temperature carbonization is carried out by heating to 1000-1700℃ at a heating rate of 5-10℃ / min and holding the temperature for 5-10 hours.

15. The preparation method according to claim 14, characterized in that, In step (S2), high-temperature carbonization involves heating to 1300-1500℃ at a rate of 5-10℃ / min and holding the temperature for 5-10 hours.

16. A sodium-ion battery anode material, comprising a hard carbon material, a conductive additive, and a binder, wherein the hard carbon material is prepared by the preparation method according to any one of claims 1-15.

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