Biomass hard carbon negative electrode material and preparation method and application thereof

Abstract

The application discloses a biomass hard carbon negative electrode material and a preparation method and application thereof, and the biomass hard carbon negative electrode material is prepared by taking papermaking black liquor as a carbon precursor, and the powder compaction density is not less than 1.15 g / cc. The preparation method of the biomass hard carbon negative electrode material comprises the following steps: (1) adding inorganic acid into the papermaking black liquor to adjust the pH to 3-6, and filtering a solid product after heating and stirring; (2) dispersing the solid product in water, and performing a heating reaction in the presence of a catalyst and hydrogen, and dialyzing to neutral after the reaction to obtain a mixture containing oligomers; (3) adding a crosslinking agent and an initiator into the mixture containing the oligomers to perform a crosslinking polymerization reaction, and obtaining a crosslinking product through washing and drying; and (4) performing carbonization treatment on the crosslinking product to obtain the hard carbon negative electrode material. The biomass hard carbon material prepared by the method has high compaction density, and can improve the energy density of a battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a biomass hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, new energy electric vehicles, and renewable energy storage. However, limited lithium resources, their uneven distribution, and high cost hinder their large-scale application in energy storage. Furthermore, the structural characteristics of the graphite anode in commercial lithium-ion batteries impede further improvements in cycle performance and rate capability. Sodium-ion batteries, with their similar energy storage mechanism to lithium-ion batteries, are expected to replace lithium-ion batteries due to their abundant resources and low cost.

[0003] Hard carbon, with its randomly oriented graphite domains, high interlayer spacing, and disordered structure of residual heteroatoms (mainly oxygen functional groups), provides more sodium ion diffusion pathways and storage sites, making it the primary anode material used in sodium-ion batteries. Hard carbon anode materials are mostly obtained by carbonization using resin or biomass as precursor carbon sources. However, resin raw materials are expensive, which does not meet the low-cost requirements of sodium-ion batteries. Hard carbon materials prepared using biomass as a precursor generally suffer from low compaction density, which is detrimental to improving energy density.

[0004] Therefore, effectively improving the compaction density of hard carbon materials prepared using biomass as a precursor carbon source is an effective way to reduce the cost of sodium-ion batteries while ensuring their energy density. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-density biomass hard carbon anode material, its preparation method, and its application. Using black liquor from papermaking waste as raw material, oligomers can be obtained by catalytic hydrogenation degradation of lignin extracted from the black liquor, followed by crosslinking and carbonization to obtain the high-density biomass hard carbon anode material.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] The first aspect of the present invention provides a hard carbon anode material, which is prepared by using papermaking black liquor as a carbon precursor; the powder compaction density of the hard carbon anode material is not less than 1.15 g / cc.

[0008] Furthermore, the hard carbon anode material is prepared by using papermaking black liquor as a carbon precursor, obtaining oligomers by catalytic hydrogenation degradation of lignin extracted from papermaking black liquor, and then cross-linking and carbonization.

[0009] A second aspect of the present invention provides a method for preparing the hard carbon anode material described in the first aspect, comprising the following steps:

[0010] (1) Add inorganic acid to papermaking black liquor to adjust pH to 3-6, heat and stir, and then filter to obtain solid product;

[0011] (2) Disperse the solid product prepared in step (1) in water, and carry out a heating reaction in the presence of a catalyst and hydrogen. After the reaction, dialyze to neutral to obtain a mixture containing oligomers.

[0012] (3) Add a crosslinking agent and an initiator to the mixture containing oligomers prepared in step (2) to carry out a crosslinking polymerization reaction, and obtain the crosslinked product after washing and drying;

[0013] (4) The crosslinking product prepared in step (3) is carbonized under an inert atmosphere to obtain the hard carbon anode material.

[0014] Further, in step (1), the inorganic acid is selected from one or more of sulfuric acid, hydrochloric acid, and nitric acid;

[0015] Furthermore, in step (1), the heating and stirring temperature is 45-60℃, and the heating and stirring time is 4-8h.

[0016] Furthermore, in step (2), the ratio of the mass of the solid product to the volume of water is in the range of 1g:10-20mL.

[0017] Further, in step (2), the catalyst is one or more of copper oxide, nickel chloride, cobalt chloride, and copper chloride.

[0018] Furthermore, in step (2), the heating reaction is carried out in a high-pressure reactor, and the flow rate of hydrogen gas is 40-120 mL / min.

[0019] Furthermore, in step (2), the temperature of the heating reaction is 170-250℃, and the heating reaction time is 4-12h.

[0020] Further, in step (2), the concentration of oligomers in the mixture containing oligomers is 20wt%-50wt%.

[0021] Further, in step (3), the crosslinking agent is selected from one or more of acrylic acid, styrene, polyacrylate, polyethylene, polyvinyl chloride, chlorinated polyethylene, EVA, and polystyrene; more preferably, the ratio of the mass of the crosslinking agent to the mass of the solid product in step (2) is in the range of 0.03-0.08:1.

[0022] Further, in step (3), the initiator comprises ammonium persulfate and an acid anhydride, wherein the acid anhydride is selected from one or more of Ningkang anhydride, maleic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, and acetic anhydride; more preferably, the ratio of the mass of the initiator to the volume of the mixture is in the range of 0.2-4 g:1 L; and the mass ratio of the ammonium persulfate to the acid anhydride is 1:1-1:2.

[0023] Furthermore, in step (3), the temperature of the crosslinking polymerization reaction is 90-150℃, and the time of the crosslinking polymerization reaction is 4-8h.

[0024] Further, in step (4), the inert atmosphere is one or more of nitrogen, argon, and helium.

[0025] Furthermore, in step (4), the carbonization treatment includes two calcination processes; wherein,

[0026] During the first stage of calcination: the heating rate is 0.5-5℃ / min, the first stage calcination temperature is 300-700℃, and the holding time is 1-10h;

[0027] During the second stage of calcination: the heating rate is 0.5-5℃ / min, the second stage calcination temperature is 1100-1400℃, and the holding time is 1-10h.

[0028] A third aspect of the present invention provides a sodium-ion battery comprising the hard carbon anode material described in the first aspect or the hard carbon anode material prepared by the preparation method described in the second aspect.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] This invention uses black liquor from papermaking waste as raw material. Lignin extracted from the black liquor is degraded by catalytic hydrogenation to obtain oligomers, which are then cross-linked and carbonized to obtain a high-compact-density biomass hard carbon anode material. This preparation method not only utilizes papermaking waste and reduces the cost of precursor carbon sources, but also effectively improves the compaction density of the biomass hard carbon anode material through catalytic hydrogenation degradation and subsequent cross-linking and carbonization. It can prepare biomass hard carbon anode materials with a powder compaction density of not less than 1.15 g / cc, thereby improving the energy density and initial efficiency of batteries using biomass hard carbon anode materials as the anode active material. Attached Figure Description

[0031] Figure 1 The image shows a SEM image of the hard carbon anode material prepared in Example 1. Detailed Implementation

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0033] Hard carbon materials prepared using biomass as a precursor generally suffer from low compaction density, which is detrimental to improving battery energy density.

[0034] To address the aforementioned issues, this invention provides a biomass hard carbon anode material with high compaction density, prepared from papermaking black liquor as a carbon precursor; the powder compaction density of the hard carbon anode material is not less than 1.15 g / cc.

[0035] Lignin is a complex phenolic compound that uses ester bonds to couple three different units—hydroxyphenyl, guaiacol, and syringyl—to form a three-dimensional network structure through carbon-carbon bonds. Compared to other biomass, lignin has a high carbon content and a high carbon yield after carbonization, making it the most promising biomass precursor. However, the compaction density of hard carbon materials prepared by directly carbonizing lignin is low, which is detrimental to improving battery energy density. To reduce the preparation cost of hard carbon materials and improve the compaction density of biomass hard carbon materials, this invention uses waste papermaking black liquor as a raw material to extract lignin as a carbon precursor (papermaking black liquor is wastewater generated from the alkaline pulping process in the papermaking industry, which contains a large amount of lignin). Lignin can be degraded into oligomers through catalytic hydrogenation, and then resin polymers are formed under the action of crosslinking agents and initiators. After carbonization, high-compact-density biomass hard carbon materials are obtained, which can be used as battery anode materials, thus improving battery energy density.

[0036] Specifically, the embodiments of this invention also provide a method for preparing high-density biomass hard carbon anode material, including the following steps:

[0037] (1) Add inorganic acid to papermaking black liquor to adjust pH to 3-6, heat and stir, and then filter to obtain solid product;

[0038] (2) Disperse the solid product prepared in step (1) in water, and carry out a heating reaction in the presence of a catalyst and hydrogen. After the reaction, dialyze to neutral to obtain a mixture containing oligomers.

[0039] (3) Add a crosslinking agent and an initiator to the mixture containing oligomers prepared in step (2) to carry out a crosslinking polymerization reaction, and obtain the crosslinked product after washing and drying;

[0040] (4) The crosslinking product prepared in step (3) is carbonized under an inert atmosphere to obtain the hard carbon anode material.

[0041] In this invention, by adding one or more inorganic acids, such as sulfuric acid, hydrochloric acid, and nitric acid, to the papermaking black liquor to adjust the pH to 3-6, lignin in the papermaking black liquor is precipitated. More preferably, after adding the inorganic acid, the mixture is heated and stirred at 45-60°C for 4-8 hours, then filtered while hot, washed, and dried to obtain the solid product lignin.

[0042] In this invention, the solid product extracted from papermaking black liquor is dispersed in water, wherein the preferred mass-to-volume ratio of the solid product to water is 1g:10-20mL, for example, 1g:10mL, 1g:11mL, 1g:12mL, 1g:13mL, 1g:14mL, 1g:15mL, 1g:16mL, 1g:17mL, 1g:18mL, 1g:19mL, 1g:20mL, etc., including but not limited to the mass-to-volume ratios listed above; then a catalyst is added, and the mixture is ultrasonically dispersed. The mixture is then transferred to a high-pressure reactor, where hydrogen gas is introduced for heating and reaction. The catalyst is preferably one or more of copper oxide, nickel chloride, cobalt chloride, and copper chloride. The hydrogen flow rate is 40-120 mL / min, for example, 40 mL / min, 60 mL / min, 80 mL / min, 100 mL / min, or 120 mL / min. More preferably, the heating temperature is 170-250°C, and the heating time is 4-12 h, for example, reacting at 200°C or 250°C for 6 h. This invention catalytically hydrogenates and depolymerizes lignin in the presence of a catalyst and hydrogen gas. Compared to other degradation methods such as acid hydrolysis, which easily leads to condensation, catalytic hydrogenation degradation is more conducive to obtaining oligomers.

[0043] In this invention, after the heating reaction, the product is dialyzed to remove impurities such as inorganic acids and catalysts. Then, the oligomer concentration is adjusted to obtain a mixture with an oligomer concentration of 20wt%-50wt%. For example, the oligomer concentration in the mixture can be adjusted to the target range by cyclone evaporation. Too high or too low a concentration of oligomers in the mixture will affect the crosslinking reaction, and consequently affect the compaction density of the carbonized crosslinked product. To obtain a hard carbon material with high compaction density, the oligomer concentration in the mixture needs to be controlled between 20wt% and 50wt%.

[0044] In this invention, oligomers obtained by catalytic hydrogenation degradation of lignin are crosslinked and polymerized under the action of a crosslinking agent and an initiator to obtain resin polymers. The crosslinking agent is selected from one or more of acrylic acid, styrene, polyacrylate, polyethylene, polyvinyl chloride, chlorinated polyethylene, EVA, and polystyrene. Preferably, the mass ratio of the crosslinking agent to the solid product of step (2) is 0.03-0.08:1, for example, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, etc., including but not limited to the mass ratios listed above. The initiator includes ammonium persulfate and anhydride, and the anhydride can be selected from Ningkang anhydride, malathion, etc. The initiator is selected from one or more of succinic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, and acetic anhydride. Preferably, the mass ratio of the initiator to the volume of the mixture is in the range of 0.2-4 g:1 L, such as 0.2 g:1 L, 0.4 g:1 L, 0.6 g:1 L, 0.8 g:1 L, 1 g:1 L, 1.5 g:1 L, 2 g:1 L, 2.5 g:1 L, 2.5 g:1 L, 3 g:1 L, 3.5 g:1 L, 4 g:1 L, etc., including but not limited to the mass-volume ratios listed above. More preferably, the mass ratio of ammonium persulfate to acid anhydride in the initiator is 1:1-2, such as 1:1, 1:1.5, 1:2, etc.

[0045] In this invention, the temperature of the crosslinking polymerization reaction is 90-150°C, and the reaction time is 4-8 hours, for example, 4 hours, 6 hours, or 8 hours at 110°C or 120°C. More preferably, the crosslinking polymerization reaction is carried out under stirring to promote the rapid and uniform polymerization of oligomers and crosslinking agents under the action of initiators.

[0046] In this invention, the crosslinked product is carbonized under an inert atmosphere to obtain a hard carbon anode material. The carbonization process can be carried out in a tube furnace, and the inert atmosphere is one or more of nitrogen, argon, and helium, with a preferred flow rate of 40-80 mL / min. The carbonization process preferably includes two calcination stages: in the first stage, the heating rate is 0.5-5 °C / min, the first stage calcination temperature is 300-700 °C, and the holding time is 1-10 h; in the second stage, the heating rate is 0.5-5 °C / min, the second stage calcination temperature is 1100-1400 °C, and the holding time is 1-10 h. For example, the temperature is increased to 700 °C at a heating rate of 2 °C / min, held for 2 h, and then increased to 1400 °C at a heating rate of 5 °C / min, held for 2 h.

[0047] The present invention also provides a sodium-ion battery comprising a hard carbon anode material prepared by the above method. Using this hard carbon anode material as the anode active material is beneficial to improving the energy density of the battery.

[0048] The present invention will be further described below with reference to the embodiments and accompanying drawings, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention.

[0049] Example 1

[0050] This embodiment relates to the preparation of a high-density biomass hard carbon anode material, specifically including the following steps:

[0051] (1) Weigh 10g of papermaking black liquor, add sulfuric acid to adjust the pH of the solution to 5, stir magnetically at 50℃ for 6h, filter while hot, wash and dry to obtain solid product.

[0052] (2) Take 5g of the solid product prepared in step (1) and disperse it in 50mL of water. Add 1g of copper oxide catalyst and ultrasonically disperse for 30min. Transfer the mixture to a stainless steel high-pressure reactor with a tetrafluoroethylene liner, introduce hydrogen gas (60mL / min), and react at 200℃ for 6h. After the reaction is complete, dialyze to neutral and adjust the product concentration to 40wt% by cyclotron evaporation to obtain a mixture containing oligomers.

[0053] (3) Take 500 mL of the mixture containing oligomers prepared in step (2), add acrylic acid (the amount of acrylic acid added is 5% of the mass of the solid product required to prepare 500 mL of the mixture containing oligomers), 0.1 g of ammonium persulfate and 0.1 g of acid anhydride, stir at 110 °C for 6 h, wash with anhydrous ethanol, freeze dry to obtain crosslinked product.

[0054] (4) Place the crosslinked product prepared in step (3) into a ceramic boat and put it into a tube furnace. Pour nitrogen gas (80 mL / min) into the furnace and heat it to 700°C at a heating rate of 2°C / min. Hold it for 2 hours. Then heat it to 1400°C at a heating rate of 5°C / min. Hold it for 2 hours to obtain a high-density biomass hard carbon anode material.

[0055] The SEM image of the hard carbon anode material prepared in this embodiment is shown below. Figure 1 As shown in the figure, hard carbon materials with different particle size distributions were obtained. Among them, the hard carbon materials with small particle size can fill the spaces between the large hard carbon particles, which is beneficial to improving the compaction density of the hard carbon anode material.

[0056] Example 2

[0057] This embodiment relates to the preparation of a high-density biomass hard carbon anode material. The only difference from Example 1 is that in step (2), the catalyst is an equal amount of nickel chloride; the rest of the operations are the same, and the high-density biomass hard carbon anode material is prepared.

[0058] Example 3

[0059] This embodiment relates to the preparation of a high-density biomass hard carbon anode material. The only difference from Example 1 is that in step (2), the reaction is carried out at 250°C for 6 hours; the rest of the operation is the same, and the high-density biomass hard carbon anode material is prepared.

[0060] Example 4

[0061] This embodiment relates to the preparation of a high-density biomass hard carbon anode material. The only difference from Example 1 is that in step (3), 500 mL of the mixture containing oligomers prepared in step (2) is taken, and 4% acrylic acid, 0.05 g ammonium persulfate and 0.1 g acid anhydride are added. After stirring at 120°C for 6 h, the mixture is washed with anhydrous ethanol and freeze-dried to obtain the crosslinked product. The remaining operations are the same, and the high-density biomass hard carbon anode material is prepared.

[0062] Example 5

[0063] This embodiment relates to the preparation of a high-density biomass hard carbon anode material. The only difference from Example 1 is that in step (3), an equal amount of polyethylene is used to replace acrylic acid; the rest of the operations are the same, and the high-density biomass hard carbon anode material is prepared.

[0064] Comparative Example 1

[0065] This comparative example relates to the preparation of a biomass hard carbon anode material, and the specific operations are as follows:

[0066] (1) Weigh 10g of papermaking black liquor, add sulfuric acid to adjust the pH of the solution to 5, stir magnetically at 50℃ for 6h, filter while hot, wash and dry to obtain solid product.

[0067] (2) Place the solid product in a ceramic boat and put it into a tube furnace. Pour nitrogen gas (80 mL / min) into the furnace and heat it to 700°C at a heating rate of 2°C / min. Hold it for 2 hours. Then heat it to 1400°C at a heating rate of 5°C / min. Hold it for 2 hours to obtain the biomass hard carbon anode material.

[0068] Comparative Example 2

[0069] This comparative example relates to the preparation of a biomass hard carbon anode material, which differs from Example 1 in the degradation method, specifically as follows:

[0070] (1) Weigh 10g of papermaking black liquor, add sulfuric acid to adjust the pH of the solution to 5, stir magnetically at 50℃ for 6h, filter while hot, wash and dry to obtain solid product.

[0071] (2) Take 5g of the solid product prepared in step (1) and disperse it in 50mL of 1M hydrochloric acid. Disperse it by ultrasonication for 30min. Transfer the mixture to a stainless steel high-pressure reactor with a tetrafluoroethylene liner, introduce hydrogen gas (60mL / min), and react at 200℃ for 6h. After the reaction is completed, dialyze to neutral and adjust the product concentration to 40wt% by cyclotron evaporation to obtain a mixture containing oligomers.

[0072] (3) Take 500 mL of the mixture containing oligomers prepared in step (2), add acrylic acid (the amount of acrylic acid added is 5% of the mass of the solid product required to prepare 500 mL of the mixture containing oligomers), 0.1 g of ammonium persulfate and 0.1 g of acid anhydride, stir at 110 °C for 6 h, wash with anhydrous ethanol, freeze dry to obtain crosslinked product.

[0073] (4) Place the crosslinked product prepared in step (3) into a ceramic boat and put it into a tube furnace. Pour nitrogen gas (80 mL / min) into the furnace and heat it to 700°C at a heating rate of 2°C / min. Hold it for 2 hours. Then heat it to 1400°C at a heating rate of 5°C / min. Hold it for 2 hours to obtain the biomass hard carbon anode material.

[0074] Performance Testing and Applications

[0075] The powder compaction density of the hard carbon anode materials prepared in the above examples and comparative examples was tested using a powder compaction density meter from Yuaneng Technology. The results are shown in Table 1 below:

[0076] Table 1

[0077] Example 1 1.16 Example 2 1.20 Example 3 1.17 Example 4 1.21 Example 5 1.15 Comparative Example 1 1.09 Comparative Example 2 1.11

[0078] As shown in Table 1, the powder compaction density test results indicate that, compared to the hard carbon material prepared directly by lignin carbonization in Comparative Example 1, the powder compaction density of the hard carbon materials prepared in Examples 1-5 using catalytic hydrogenation degradation followed by crosslinking polymerization significantly improves the lignin-based carbon precursor source, thus contributing to the improvement of battery energy density. While the hard carbon material prepared in Comparative Example 2 through acid hydrolysis followed by crosslinking polymerization and carbonization shows some improvement in powder compaction density compared to Comparative Example 1, the improvement is not significant and is considerably lower than the powder compaction density of the hard carbon material prepared in Example 1.

[0079] Sodium-ion batteries were prepared using the hard carbon anode materials prepared in Examples 1-5 and Comparative Examples 1 and 2 as anode active materials, respectively. The initial coulombic efficiency of each battery was tested. The specific operation was as follows: the hard carbon anode material was mixed with conductive carbon black, carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 93.5:2.5:1.6:2.4. After adding deionized water and mixing evenly, a negative electrode slurry was obtained and coated on copper foil to obtain a negative electrode sheet.

[0080] Using a sodium metal sheet as the counter electrode and 1.0 mol / L NaPF6 / EC (ethylene carbonate) + DMC (dimethyl carbonate) (EC to DMC ratio 1:1) as the electrolyte, CR2032 button cells were assembled in an argon glove box.

[0081] The electrochemical performance of the prepared CR2032 button cells was tested using the Land battery testing system. The specific testing method was as follows: the cells were discharged to 0V at a discharge rate of 0.05C, and the discharge capacity at this point was recorded as the initial discharge capacity; then, they were charged to 2V at a charge rate of 0.1C, and the charge capacity at this point was recorded as the initial charge capacity; the initial coulombic efficiency was calculated as (initial charge capacity / initial discharge capacity) × 100%. The test results are shown in Table 2.

[0082] Table 2

[0083]

[0084] As shown in Table 2, compared with the hard carbon anode material prepared by directly calcining lignin (Comparative Example 1) and the hard carbon anode material prepared by acid hydrolysis and cross-linking carbonization of lignin (Comparative Example 2) as the anode active material, the button batteries constructed using the hard carbon anode material with high powder compaction density prepared in Examples 1-5 have higher initial charge capacity and better initial coulombic efficiency. Among them, the initial coulombic efficiency of the button batteries prepared using the hard carbon anode material prepared in Examples 3 and 4 as the anode active material can reach more than 90%.

[0085] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a hard carbon anode material, characterized in that, Includes the following steps: (1) Add inorganic acid to papermaking black liquor to adjust the pH to 3-6, heat and stir, and then filter to obtain solid product; (2) Disperse the solid product prepared in step (1) in water and heat it in the presence of a catalyst and hydrogen. After the reaction, dialyze it to neutral to obtain a mixture containing oligomers. The catalyst is selected from one or more of copper oxide, nickel chloride, cobalt chloride and copper chloride. (3) A crosslinking agent and an initiator are added to the mixture containing oligomers prepared in step (2) to carry out a crosslinking polymerization reaction. The mixture is washed and dried to obtain a crosslinked product. The crosslinking agent is acrylic acid. The initiator contains ammonium persulfate and acid anhydride. (4) The crosslinked product prepared in step (3) is carbonized under an inert atmosphere to obtain the hard carbon anode material.

2. The preparation method according to claim 1, characterized in that, In step (1), the inorganic acid is selected from one or more of sulfuric acid, hydrochloric acid, and nitric acid; The heating and stirring temperature is 45-60 ℃, and the heating and stirring time is 4-8 h.

3. The preparation method according to claim 1, characterized in that, In step (2), at least one of the following characteristics must be satisfied: (1) The ratio of the mass of the solid product to the volume of water is in the range of 1 g: 10-20 mL; (2) The concentration of oligomers in the mixture containing oligomers is 20 wt%-50 wt%.

4. The preparation method according to claim 1, characterized in that, In step (2), the heating reaction is carried out in a high-pressure reactor, and the flow rate of hydrogen gas is 40-120 mL / min; The heating reaction is carried out at a temperature of 170-250 °C for 4-12 h.

5. The preparation method according to claim 1, characterized in that, In step (3), the ratio of the mass of the crosslinking agent to the mass of the solid product in step (2) is in the range of 0.03-0.08:1; The anhydride is selected from one or more of Ningkang anhydride, maleic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, and acetic anhydride; the ratio of the mass of the initiator to the volume of the mixture is in the range of 0.2-4 g: 1 L.

6. The preparation method according to claim 1, characterized in that, The mass ratio of ammonium persulfate to acid anhydride is 1:1 to 1:

2.

7. The preparation method according to claim 1, characterized in that, In step (3), the temperature of the crosslinking polymerization reaction is 90-150 °C, and the time of the crosslinking polymerization reaction is 4-8 h.

8. The preparation method according to claim 1, characterized in that, In step (4), the carbonization treatment includes two calcination processes; wherein, During the first stage of calcination: the heating rate is 0.5-5 ℃ / min, the first stage calcination temperature is 300-700 ℃, and the holding time is 1-10 h; During the second stage of calcination: the heating rate is 0.5-5 ℃ / min, the second stage calcination temperature is 1100-1400 ℃, and the holding time is 1-10 h.

9. A sodium-ion battery, characterized in that, The hard carbon anode material prepared by the preparation method according to any one of claims 1-8.

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