CN118545702A - Method for preparing hard carbon, negative electrode active material, and sodium ion battery - Google Patents

Abstract

The application relates to the technical field of sodium ion batteries, and discloses a method for preparing hard carbon, which comprises the following steps: mixing lignin, a soft template agent and a hard template agent, and performing ball milling treatment to obtain a mixture; in a first protective atmosphere, carrying out first carbonization treatment on the mixture to obtain a composite material; and performing second carbonization treatment on the composite material in a second protective atmosphere to obtain a hard carbon material, wherein the temperature of the second carbonization treatment is T ₂, and the temperature of the first carbonization treatment is T ₁,T₂-T₁ & gt300 ℃. The hard carbon material prepared by the method has better electrochemical properties.

Description

Method for preparing hard carbon, negative electrode active material, and sodium ion battery

Technical Field

The present application relates to the technical field of sodium ion batteries, and in particular, to a method for preparing hard carbon, a negative electrode active material, and a sodium ion battery.

Background Art

At present, energy is transforming towards green development, and green energy such as wind energy, solar energy, tidal energy, and geothermal energy are developing rapidly. However, intermittent power generation has a great impact on the power grid, and it is necessary to equip corresponding electrochemical energy storage power stations to store and convert energy efficiently. At present, lithium-ion batteries have been successfully commercialized as energy storage batteries, but lithium resources are unevenly distributed. In this context, it is crucial to develop new energy storage systems with low costs and excellent performance. Due to its abundant sodium reserves, environmental friendliness, and similar electrochemical properties to lithium-ion batteries, sodium-ion batteries are considered to be an ideal choice for the new generation of energy storage devices. Sodium-ion batteries show very broad application prospects in the field of energy storage and need further development and research.

Summary of the invention

In a first aspect of the present application, a method for preparing hard carbon is proposed, comprising: mixing lignin, a soft template, and a hard template, and performing ball milling to obtain a mixture; performing a first carbonization treatment on the mixture in a first protective atmosphere to obtain a composite material; performing a second carbonization treatment on the composite material in a second protective atmosphere to obtain a hard carbon material, wherein the temperature of the second carbonization treatment is T ₂ , the temperature of the first carbonization treatment is T ₁ , and T ₂ -T ₁ >300°C.

Lignin has a variety of functional groups such as carbonyl, conjugated ester, phenolic hydroxyl, and aromatic groups, and can be used as a good modification basis. The three-dimensional aromatic hydrocarbon structure of lignin makes it useful for synthesizing porous carbon materials. Adding soft and hard templates and treating lignin using the template method can generate a porous structure, and then further through the second carbonization treatment to obtain a porous hard carbon material.

In some embodiments, the method further comprises: washing the lignin; and/or acid-treating the composite material.

The soluble impurities and ash in lignin can be removed by washing treatment, thus improving the purity of lignin. The unreacted template in the composite material can be removed by acid treatment, which is beneficial for further processing of the composite material.

In some embodiments, the lignin, the soft template, and the hard template are mixed in a mass ratio of 1:(0.5-2):(0.5-2); and/or the hard template includes at least one of zinc oxide and magnesium oxide; and/or the soft template includes at least one of furan-based polyester, furan-based polyamide, furan-based polyurethane, and furan-based polyimide.

In some embodiments, the soft template has a molecular weight of 10,000-100,000.

Within the aforementioned mass ratio range of lignin to the template, the prepared hard carbon material has good electrochemical properties and structural stability.

In some embodiments, the temperature of the first carbonization treatment is 600°C-800°C, the time is 2h-4h, and the heating rate is 2°C/min-10°C/min; and/or the temperature of the second carbonization treatment is 1100°C-1400°C, the time is 2h-4h, and the heating rate is 2°C/min-10°C/min.

When the conditions of the first carbonization treatment are within the aforementioned range, the lignin and the template are mixed and pyrolyzed, and the molecules of the lignin are changed; when the conditions of the second carbonization treatment are within the aforementioned range, a hard carbon material with a porous structure and a stable pore structure can be prepared.

In some embodiments, the first protective atmosphere and the second protective atmosphere independently include _N2 and an inert gas, respectively; and/or, the rotation speed of the ball milling treatment is 300r/min-500r/min, and the time is 120min-240min.

In the protective gas atmosphere, the occurrence of side reactions such as oxidation reaction during the pyrolysis of lignin can be reduced. Within the aforementioned ball milling speed and time range, lignin, soft template agent, and hard template agent can be fully mixed.

In some embodiments, the method further includes: the concentration of the acidic solution in the acid treatment is 0.5 mol/L-2 mol/L, and the time of the acid treatment is 2h-10h; and/or, the acidic solution in the acid treatment includes a hydrochloric acid solution; and/or, after the acid treatment, further includes drying the composite material treated with the acid, the temperature of the drying treatment is 60°C-100°C, and the time is 3h-9h.

The aforementioned acid treatment can fully remove the metal oxide particles in the composite material, and obtain a composite material with a high purity and a porous structure. The drying treatment conditions are within the aforementioned temperature and time range, and the composite material can be fully dried, which is conducive to the second carbonization treatment.

In some embodiments, the cleaning treatment includes: cleaning the lignin in water and an acidic solution in sequence; and/or, after the cleaning treatment, further including drying the cleaned lignin, the drying temperature is 60°C-80°C, and the drying time is 20h-30h.

Washing lignin with water and acid solution in sequence can improve the composition of functional groups on the surface of lignin, thereby improving the performance of the prepared hard carbon material. After washing, drying is performed to fully dry the lignin and reduce the free water content on its surface.

In a second aspect of the present application, the present application proposes a negative electrode active material, comprising a hard carbon material prepared by the aforementioned method.

The hard carbon material prepared by the above method has a porous molecular structure, and the pore structure is highly stable and not prone to collapse, and can be used as a negative electrode active material for sodium ion batteries.

In a third aspect of the present application, the present application proposes a sodium ion battery comprising the aforementioned negative electrode active material.

Therefore, the sodium ion battery using the negative electrode active material has higher energy density and initial charge and discharge efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

FIG1 is a scanning electron microscope image of a hard carbon material in one embodiment of the present application;

FIG2 is a scanning electron microscope image of a hard carbon material in one embodiment of the present application;

FIG3 is an XRD diagram of a hard carbon material in one embodiment of the present application;

FIG4 is a charge and discharge curve diagram of a sodium ion battery made of hard carbon material in one embodiment of the present application.

DETAILED DESCRIPTION

The embodiments of the present application are described in detail below. Examples of the embodiments are shown in the drawings, but unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; unless otherwise specified, the numerical values of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this application).

The terms "including" and "having" in the specification and claims of the present application and any modifications thereof are open expressions, that is, including the contents specified in the present application but not excluding other contents.

In the description of this application, regardless of whether the words "about" or "approximately" are used, all the numbers disclosed herein are approximate values. The value of each number may differ by less than 10% or a reasonable difference considered by those skilled in the art, such as 1%, 2%, 3%, 4% or 5%.

"Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

In the research process of sodium ion batteries, carbon-based materials have become the preferred target for sodium storage negative electrode active materials because of their advantages such as wide sources, rich resources, diverse structures and long life. Hard carbon materials have larger interlayer spacing, more nanopores, and more defect sites, can store more sodium ions, and show higher specific capacity. Therefore, hard carbon materials are one of the most promising negative electrode active materials for sodium ion batteries. However, the metal or non-metallic impurity elements contained in hard carbon materials will consume sodium ions and reduce the cycle performance of sodium ion batteries; and the specific surface area of hard carbon materials is too large, so that the pore structure and interlayer spacing do not match the diameter of sodium ions, resulting in low first coulomb efficiency, poor rate performance and unsatisfactory cycle performance of sodium ion batteries, which affects the development of sodium ion batteries. The present invention proposes a method for preparing hard carbon. The hard carbon material prepared by the method has a porous structure with better pore size and structural strength. When the hard carbon material is used as the negative electrode active material, the battery can have a larger energy density and first cycle efficiency.

In a first aspect of the present application, a method for preparing hard carbon is proposed, comprising: mixing lignin and a template, and performing ball milling to obtain a mixture; performing a first carbonization treatment on the mixture in a first protective atmosphere to obtain a composite material; performing a second carbonization treatment on the composite material in a second protective atmosphere to obtain a hard carbon material, wherein the temperature of the second carbonization treatment is T ₂ , the temperature of the first carbonization treatment is T ₁ , and T ₂ -T ₁ >300°C.

Lignin molecules contain a variety of functional groups, with a variety of unit connections and acylation or cross-linking structures, so they have a good basis for modification. Lignin can be divided into syringyl propane units (S-type lignin), guaiacyl propane units (G-type lignin) and p-hydroxyphenyl propane units (H-type lignin) according to the number of methoxy groups connected to the benzene ring in the phenylpropane units contained therein. Among them, G-type and S-type lignin, in particular, can form methyl aryl ether bonds due to the large number of methoxy groups on their phenylpropane units. The molecules can be connected through ether bonds or through carbon-carbon bonds to form a three-dimensional network-like molecular structure, which can have excellent electrochemical properties after further modification. The template agent acts as a scaffold, which can support and restrict the spatial structure. After lignin, soft template agents, and hard template agents are mixed, the template agent can be used to form a microscopic three-dimensional structure containing pores, tunnels, etc. built by the template agent in the mixture of the two. The soft-hard template composite method that matches and uses soft templates and hard templates at the same time combines the advantages of hard templates and soft templates, and can design negative electrode materials with complex structures and excellent performance. The hard template method can provide precise spatial confinement and regulation, while the soft template method has better plasticity and easy removability. The combination of the two can achieve more precise structural control. Specifically, lignin is mixed with a template. After the first carbonization treatment, the lignin can be initially carbonized to form a microstructure with pores, and the morphology and size of the structure are restricted by the template; after the second carbonization treatment, the polymer components in the lignin can be further carbonized, so that the hard carbon material finally obtained can maintain a three-dimensional network structure containing pores and tunnels. Controlled by the template, the pore size of the structure matches the diameter of the sodium ions, which helps the sodium ions to move relatively freely therein.

In some embodiments, the method further comprises: washing the lignin.

The three-dimensional network structure of the lignin molecule itself may cause some impurities to be mixed in the lignin, which may interfere with the carbonization process. The impurities in the lignin can be removed from the lignin raw materials through cleaning treatment, thereby improving the purity of the reactants.

In some embodiments, the method further comprises: subjecting the composite material to an acid treatment.

After the composite material is formed by mixing the soft template and the hard template with lignin through the first carbonization treatment, the carbon thermal reaction can reduce the template zinc oxide to elemental zinc, and part of the elemental zinc can be taken away from the composite material by hot air during the carbonization process. However, some elemental zinc and incompletely reacted zinc oxide remain in the composite material. The elemental zinc and incompletely reacted zinc oxide can be converted into soluble solutes through acid treatment, and separated from the composite material with the acidic solution, thereby reducing the adverse effects of impurities on the second carbonization treatment.

In some embodiments, the lignin is mixed with the soft template and the hard template in a mass ratio of 1:(0.5-2):(0.5-2); and/or the hard template includes at least one of zinc oxide and magnesium oxide; and/or the soft template includes at least one of furan-based polyester, furan-based polyamide, furan-based polyurethane, and furan-based polyimide.

In some embodiments, the soft template has a molecular weight of 10,000-100,000.

By controlling the amount of template used, the shape and proportion of the holes and channels supported by the template in the mixture of lignin and template are controlled, and thus the size, morphology and structure of the microscopic pores of the material prepared by the template method can be controlled. After lignin is mixed with the template, the pores in its three-dimensional structure can still be maintained after pyrolysis. Taking into account the electrochemical properties, structural stability and preparation cost of the hard carbon material prepared, a more ideal effect can be obtained when the mass ratio of lignin to the template is within the aforementioned range.

As an example, the mass ratio of lignin to the zinc oxide and the furan-based polyester may be 1:1:1.

In some embodiments, the temperature _T1 of the first carbonization treatment is 600°C-800°C, and the time is 2h-4h.

The first carbonization treatment at the aforementioned treatment time and temperature helps to release the hydrogen atoms in the lignin in a volatile form, increase the active sites on the surface of the material, promote organic cross-linking between molecules, increase the disorder of the structure, facilitate the migration and diffusion of Na ⁺ , and increase the sodium storage capacity.

In some embodiments, _T1 is 600°C-800°C.

As an example, _T1 may be 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, or 800°C.

In some embodiments, the temperature _T2 of the second carbonization treatment is 1100°C-1400°C, and the time is 2h-4h.

As examples, _T2 may be 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, or 1400°C.

When the second carbonization treatment is carried out at the aforementioned treatment time and treatment temperature, the microstructure of the composite material can be adjusted and optimized by further carbonization to obtain a hard carbon material with a suitable interlayer spacing.

In some embodiments, the heating rates of the first carbonization treatment and the second carbonization treatment are independently 2° C./min-10° C./min.

During the carbonization process, when the heating rate is within the aforementioned range, the carbonized polymer, namely the lignin used in the present invention, can reduce the degree of side reactions such as oxidation reaction and decomposition reaction that may occur during the carbonization process.

In some embodiments, the first protective atmosphere and the second protective atmosphere independently include _N2 and an inert gas, respectively; and/or, the rotation speed of the ball milling treatment is 300r/min-500r/min, and the time is 120min-240min.

In some embodiments, the carbonization treatment equipment is a high temperature tube furnace.

In some embodiments, the method further includes: the concentration of the acidic solution in the acid treatment is 0.5 mol/L-2 mol/L, and the time of the acid treatment is 2h-10h; and/or, the acidic solution in the acid treatment includes a hydrochloric acid solution; and/or, after the acid treatment, further includes drying the composite material treated with the acid, the temperature of the drying treatment is 60°C-100°C, and the time is 3h-9h.

The composite material is subjected to acid treatment, and the residual metal oxides in the composite material can be removed by soaking in an acid solution, and then washed with deionized water to neutrality, and then dried.

In some embodiments, the acidic solution in the acid treatment comprises hydrochloric acid.

In some embodiments, the cleaning treatment includes: cleaning the lignin in water and an acidic solution in sequence; and/or, after the cleaning treatment, further including drying the cleaned lignin, the drying temperature is 60°C-80°C, and the drying time is 20h-30h.

In some embodiments, when the lignin is washed with an acidic solution, the volume of the acidic solution is 5 mL based on the mass of lignin being 1 g, wherein the concentration of the acidic solution is 0.5 mol/L-2 mol/L.

In some embodiments, when the lignin is washed with an acidic solution, the acidic solution includes a hydrochloric acid solution with a concentration of 1 mol/L.

In some embodiments, the lignin is washed with deionized water and an acid solution in sequence using a funnel, and the process is repeated three times. A glass rod is used to assist in stirring to ensure sufficient washing. After washing, the lignin is dried in an oven.

Water washing can preliminarily remove soluble impurities and ash in lignin and improve purity; acid washing can further remove inorganic impurities in lignin and improve the purity and stability of lignin. In addition, acid washing can change the functional group composition of lignin surface, increase the number of oxygen-containing functional groups, improve the surface chemical properties of hard carbon materials, and improve the compatibility and stability of hard carbon materials with other materials.

In a second aspect of the present application, the present application proposes a negative electrode active material, comprising the hard carbon material.

The hard carbon material proposed in the present invention, referring to FIG. 1 and FIG. 2 , is made of lignin and has an irregular shape, an uneven particle size of 2 μm-25 μm, a relatively smooth surface, and moderate pores.

In a third aspect of the present application, the present application proposes a sodium ion battery, comprising the sodium ion battery negative electrode active material.

In some embodiments, the hard carbon material, carbon black and binder are mixed and ground in a mass ratio of 80:10:10, and the binder is carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) to obtain a slurry; the slurry is coated on a copper foil and vacuum dried to obtain a negative electrode sheet of a sodium ion battery.

The scheme of the present application is described below by specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are indicated in the examples, the technology or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products that can be obtained by commercial purchase.

Example 1

Lignin treatment: A certain amount of lignin was washed with water and 1 mol/L hydrochloric acid solution in turn, and the process was repeated three times. The mixture was stirred with a glass rod and dried in an oven at 60°C for 24 h to obtain lignin powder.

Adding soft and hard templates: The lignin powder in step 1 is mixed evenly with zinc oxide and furan-based polyester powder, weighed in a ratio of 1:1:1, and ball-milled at a speed of 300 r/min for 120 min to obtain a mixed powder;

First carbonization treatment: put the mixed powder into a tube furnace and pyrolyze and carbonize at 600℃ in a _N2 atmosphere at a heating rate of 5℃/min for 2 h to obtain a composite material;

Acid treatment: remove ZnO, place the obtained composite material in an acidic solution with a concentration of 1 mol/L for 2 h; soak to remove metal oxides, then wash with deionized water until neutral, and dry at a drying temperature of 100°C for 3 h.

Second carbonization treatment: the composite material was placed in a tubular furnace and pyrolyzed and carbonized at 1300°C in a _N2 atmosphere at a heating rate of 5°C/min for 2 h to obtain a hard carbon material.

Example 2

Example 2 is consistent with Example 1, except that the temperature of the second carbonization treatment is 1200°C.

Example 3

Example 3 is consistent with Example 1, except that the temperature of the second carbonization treatment is 1500°C.

Example 4

Example 4 is consistent with Example 1, except that, in the acid treatment, the acidic solution is a hydrochloric acid solution with a concentration of 4 mol/L.

Example 5

Example 5 is consistent with Example 1, except that when the soft and hard templates are added, the ball milling time is 4 h.

Example 6

Example 6 is consistent with Example 1, except that when the soft and hard templates are added, the ratio of lignin to zinc oxide and furan-based polyester is 1:2:2.

The aforementioned hard carbon material is used as the negative electrode active material to assemble a button cell. The specific steps are as follows:

The hard carbon material was mixed with carbon black, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of 80:10:5:5, and mixed evenly in a mortar with deionized water as a dispersant to form a slurry. The slurry was evenly coated on a copper foil with a coater, placed in a vacuum oven at 80°C for 12 h, and then used as a punching machine to prepare a negative electrode with a diameter of 14 mm. The glass fiber disc was used as a diaphragm, the sodium metal sheet was used as the counter electrode and the reference electrode, and the electrolyte was sodium hexafluorophosphate dissolved in diethylene glycol dimethyl ether. The sodium ion battery was assembled in a glove box filled with high-purity argon according to the structure of the CR2032 standard button cell.

The sodium ion battery assembled in the above-mentioned embodiment was charged and discharged on a battery test platform at a current density of 50 mA·g ^-1 . The results are shown in Table 1.

Table 1

Referring to Figure 3, the XRD diagram of the hard carbon material in Example 1 shows that the diffraction peak half-width of the (002) crystal plane of the carbon material is large and the angle is small, indicating that the hard carbon material has a high degree of disorder in the crystallites and a large interlayer spacing, which is conducive to the deintercalation of sodium ions.

4 , the sodium ion battery in Example 1 has a high discharge capacity of 388 mAh·g ^-1 , a first cycle discharge capacity of 446.4 mAh·g ^-1 , a charge capacity of 388.2 mAh·g ^-1 , and a first charge and discharge efficiency of 87%.

The test results show that the carbon material with a specific structure obtained by the present invention is beneficial to improving the capacity of the sodium ion battery and improving the initial charge and discharge efficiency.

In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. "First feature" and "second feature" may include one or more of the features.

In the description of the present application, "A and/or B" may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for examples and may be any technical feature connected by "and/or" in the present application.

In the description of this application, "same chemical composition" should be understood in a broad sense, that is, the main components of the two have the same chemical composition, or the chemical composition of the two is basically the same, and may have errors within the allowable range in the field that are understandable to those skilled in the art or contain impurities within the allowable range.

In the present application, the writing order of each step does not mean a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (10)

1. A method for preparing hard carbon, comprising: The lignin, the soft template and the hard template are mixed and ball-milled to obtain a mixture; In a first protective atmosphere, subjecting the mixed material to a first carbonization treatment to obtain a composite material; In a second protective atmosphere, the composite material is subjected to a second carbonization treatment to obtain a hard carbon material. The temperature of the second carbonization treatment is T ₂ , the temperature of the first carbonization treatment is T ₁ , and T ₂ -T ₁ >300°C. 2. The method according to claim 1, further comprising: washing the lignin; and/or, The composite material is subjected to an acid treatment. 3. The method according to claim 1 or 2, characterized in that: The lignin, the soft template, and the hard template are mixed in a mass ratio of 1:(0.5-2):(0.5-2); and/or, The hard template comprises at least one of zinc oxide and magnesium oxide; and/or, The soft template includes at least one of furan-based polyester, furan-based polyamide, furan-based polyurethane and furan-based polyimide. 4. The method according to claim 1 or 2, characterized in that: The temperature of the first carbonization treatment is 600°C-800°C, the time is 2h-4h, and the heating rate is 2°C/min-10°C/min. 5. The method according to claim 1 or 2, characterized in that: The temperature of the second carbonization treatment is 1100°C-1400°C, the time is 2h-4h, and the heating rate is 2°C/min-10°C/min. 6. The method according to claim 1 or 2, characterized in that The first protective atmosphere and the second protective atmosphere independently include _N2 and an inert gas; and/or, The ball milling process is performed at a rotation speed of 300 r/min-500 r/min and a time of 120 min-240 min. 7. The method according to claim 2, further comprising: The concentration of the acid solution in the acid treatment is 0.5 mol/L-2 mol/L, and the time of the acid treatment is 2h-10h; and/or, The acidic solution in the acid treatment includes a hydrochloric acid solution; and/or, After the acid treatment, the method further comprises drying the composite material after the acid treatment, wherein the drying temperature is 60° C.-100° C. and the drying time is 3 h-9 h. 8. The method according to claim 2, characterized in that the washing treatment comprises: washing the lignin in water and an acid solution in sequence; and/or, After the cleaning process, the method further comprises drying the cleaned lignin, wherein the drying temperature is 60° C.-80° C., and the drying time is 20 h-30 h. 9. A negative electrode active material, characterized in that it comprises a hard carbon material prepared by the method according to any one of claims 1 to 8. 10. A sodium ion battery, characterized by comprising the negative electrode active material according to claim 9.