Preparation method and application of high-capacity biomass hard carbon material

Abstract

The invention relates to the technical field of sodium ion batteries, and provides a preparation method and application of a high-capacity biomass hard carbon material, and the preparation method comprises the following steps: mixing a biomass hard carbon precursor with polyamide acid, and carrying out two-step carbonization treatment to obtain a closed-pore structure hard carbon material with excellent pore size and structural strength. Wherein polyamide acid is used as a pore-forming agent and has dual effects with a pore-closing agent, so that a rich pore-closing structure is formed. The closed-cell structure of the obtained hard carbon material is matched with the diameter of sodium ions, and the hard carbon material has high platform capacity, relatively high first charge-discharge efficiency and wide application range.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a method for preparing a high-capacity biomass hard carbon material and its application. Background Art

[0002] Driven by the country's dual carbon goals, 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 there are problems such as uneven distribution of lithium resources and poor high and low temperature performance. In this context, it is crucial to develop a new energy storage system with low cost 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, and sodium-ion batteries have good application advantages in low temperature environments and high-rate charge and discharge. Sodium-ion batteries show very broad application prospects in the field of energy storage, which needs further development and research.

[0003] In the research process of sodium-ion batteries, carbon-based materials have become the first choice 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, which 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. Summary of the invention

[0004] Based on the shortcomings of existing hard carbon materials, the present invention proposes a method for preparing high-capacity biomass hard carbon materials, aiming to make the prepared hard carbon material have a closed-pore structure with excellent pore size and structural strength, so that when the hard carbon material is used as the negative electrode active material, the battery can have a larger energy density and first coulombic efficiency.

[0005] In order to achieve the purpose, the present invention adopts the following technical scheme:

[0006] In a first aspect of the present invention, the present invention provides a method for preparing a high-capacity biomass hard carbon material, comprising the following steps:

[0007] S1. Pretreatment: dissolving the biomass carbon source in water and an acid solution in sequence for washing, and then drying to obtain a biomass hard carbon precursor powder;

[0008] S2, ball milling and mixing: ball milling the biomass hard carbon precursor powder and the polyamic acid powder to uniformly mix to obtain a mixed powder;

[0009] S3, pre-carbonization: performing a first carbonization treatment on the mixed powder in a first protective atmosphere to obtain a composite material;

[0010] S4, post-processing: in a second protective atmosphere, the composite material obtained in step S3 is further subjected to a second carbonization treatment to obtain a hard carbon material.

[0011] In the technical solution of the present invention: the biomass carbon source has multiple functional groups such as carbonyl, conjugated ester, phenolic hydroxyl, aromatic, etc., has multiple unit connections and acylation or cross-linking structures, and thus has a good modification basis, and its three-dimensional aromatic hydrocarbon structure enables it to be used to synthesize porous carbon materials. A porous structure can be generated by adding a pore-forming agent and treating the biomass carbon source, and further a closed-cell agent and a second carbonization treatment can be used to obtain a hard carbon material with a closed-cell structure. Preferably, the biomass carbon source includes at least one of coconut shells, starch, bamboo powder, straw, walnut shells, potatoes and wheat.

[0012] Preferably, in step S1: the acidic solution includes at least one of a hydrochloric acid solution and a sulfuric acid solution, the concentration of the acidic solution is 0.5-2 mol / L, and the biomass carbon source is treated in the acidic solution for 2-10 hours; the drying temperature is 60-100°C, and the drying time is 20-30 hours. Washing the biomass carbon source with water and an acidic solution in turn can improve the surface functional group composition of the biomass hard carbon precursor, thereby improving the performance of the prepared hard carbon material. After the washing treatment, a drying treatment is performed, and the biomass hard carbon precursor is fully dried to reduce the free water content on its surface.

[0013] Preferably, in step S2: the polyamic acid includes at least one of aliphatic polyamic acid, furan polyamic acid and aromatic polyamic acid; the biomass hard carbon precursor powder and the polyamic acid powder are mixed in a mass ratio of 1:(0.1-0.5). Within the mass ratio range of the precursor powder and the polyamic acid powder, the electrochemical performance and structural stability of the prepared hard carbon material are both good.

[0014] Preferably, in step S2, the ball milling speed is 300-500 r / min and the time is 120-240 min. Within the speed and time range of the ball milling treatment, the precursor powder and the polyamic acid can be fully mixed.

[0015] Preferably: in step S3, the temperature of the first carbonization treatment is 400-800°C, the time is 2-4h, and the heating rate is 2-10°C / min. In step S4, the temperature of the second carbonization treatment is 1100-1500°C, the time is 2-4h, and the heating rate is 2-10°C / min. When the conditions of the first carbonization treatment are within the aforementioned range, the biomass hard carbon precursor powder and the pore-forming agent are mixed and pyrolyzed, and the molecules of the precursor change; when the conditions of the second carbonization treatment are within the aforementioned range, the pore-closing agent is subjected to high-temperature decomposition to prepare a hard carbon material with closed pores and a stable structure. Among them, the polyamic acid powder acts as a pore-forming agent in the first carbonization treatment and as a pore-closing agent in the second carbonization treatment.

[0016] Preferably, the first protective atmosphere and the second protective atmosphere each independently comprise N 2 In the protective gas atmosphere, the occurrence of side reactions such as oxidation reaction during the pyrolysis of the biomass hard carbon precursor can be reduced.

[0017] In the second aspect of the present invention, the present invention provides a negative electrode active material, including the hard carbon material prepared by the above method. The hard carbon material prepared by the above method has a closed-pore structure in its 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 a sodium ion battery.

[0018] In a third aspect of the present invention, the present invention provides a sodium ion battery, comprising the aforementioned negative electrode active material. Thus, the sodium ion battery using the negative electrode active material has a higher energy density and initial charge and discharge efficiency.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The present invention proposes a new method for preparing hard carbon materials, which uses a biomass hard carbon precursor mixed with polyamic acid, and obtains a closed-pore hard carbon material with excellent pore size and structural strength through a two-step carbonization treatment, wherein the polyamic acid acts as a pore-forming agent and a closed-pore agent to form a rich closed-pore structure. The closed-pore structure of the hard carbon material obtained by the present invention matches the diameter of sodium ions, has a high platform capacity and a high first charge and discharge efficiency, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0022] Figure 1 This is a scanning electron microscope image of the carbon material with an open-pore structure that has not undergone the second carbonization treatment in Example 1 of the present invention;

[0023] Figure 2This is a scanning electron microscope image of the hard carbon material obtained through the second carbonization treatment in Example 1 of the present invention;

[0024] Figure 3 is the XRD pattern of the hard carbon material in Example 1 of the present invention;

[0025] Figure 4 This is a charge and discharge curve diagram of the sodium ion battery assembled with hard carbon material in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides a method for preparing a high-capacity biomass hard carbon material, comprising the following steps:

[0028] S1. Pretreatment: dissolving the biomass carbon source in water and an acid solution in sequence for washing, and then drying to obtain a biomass hard carbon precursor powder;

[0029] S2, ball milling and mixing: ball milling the biomass hard carbon precursor powder and the polyamic acid powder to uniformly mix to obtain a mixed powder;

[0030] S3, pre-carbonization: performing a first carbonization treatment on the mixed powder in a first protective atmosphere to obtain a composite material;

[0031] S4, post-treatment: in a second protective atmosphere, the composite material obtained in step S3 is further subjected to a second carbonization treatment to obtain a hard carbon material. The temperature of the second carbonization treatment is T2, the temperature of the first carbonization treatment is T1, and T2-T1>300°C.

[0032] Biomass carbon source molecules contain a variety of functional groups, with a variety of unit connections and acylation or cross-linking structures, and thus have a good basis for modification. Biomass carbon sources can be divided into syringyl propane units (S-type biomass hard carbon precursors), guaiacyl propane units (G-type biomass hard carbon precursors) and p-hydroxyphenyl propane units (H-type biomass hard carbon precursors) according to the number of methoxy groups connected to the benzene ring in the phenylpropane units contained therein. Among them, especially G-type and S-type biomass hard carbon precursors, because of the large number of methoxy groups on their phenylpropane units, methyl aromatic ether bonds can be formed, and the molecules can be connected through ether bonds, or through carbon-carbon bonds, thereby forming a three-dimensional network-like molecular structure, which can have excellent electrochemical properties after further modification.

[0033] After the biomass hard carbon precursor and polyamic acid are mixed, their characteristics can be used to form a microscopic three-dimensional structure. By taking advantage of the advantages of polyamic acid, negative electrode materials with complex structures and excellent performance can be designed. Specifically, the biomass hard carbon precursor is mixed with polyamic acid, and after the first carbonization treatment, the polyamic acid undergoes a dehydration cyclization reaction. The amide group in the polyamic acid molecule loses water molecules under the action of heat to form an imide ring. The water molecules then escape from the reaction system in the form of gas. As the temperature rises, the dehydration cyclization reaction gradually accelerates until the polyamic acid is completely converted into polyimide. In the process, the bio-based hard carbon material is activated once by the escaped water molecules, and is initially carbonized to form a microstructure with pores; after the second carbonization treatment, the polymer in the biomass hard carbon precursor is activated once, and the polymer in the biomass hard carbon precursor is activated once, and then ... The physical components can be further carbonized, and the chemical bonds in the polyimide molecular chain are gradually broken, resulting in the depolymerization and degradation of the polymer chain, which will release a variety of small molecule gases for secondary activation of the bio-based hard carbon material. The unformed polyamic acid will also undergo a high-temperature decomposition reaction and may produce gas. After high-temperature pyrolysis, carbonized products will be formed to seal the pores formed by the two activations of the bio-based hard carbon material, so that the hard carbon material finally obtained can maintain a rich closed-pore structure. The pore size of this structure matches the diameter of the sodium ions, which helps the sodium ions to move relatively freely in it.

[0034] A pore former is an additive that can promote the formation of a pore structure inside a material. During the preparation of hard carbon materials, the pore former produces a pore structure inside the material through a specific chemical reaction or physical action, which can affect the material's specific surface area, porosity, pore size distribution and other properties. A closed-cell agent is a chemical additive that can promote the formation of a closed-cell structure inside the material. Through a specific chemical reaction or physical action, a closed pore structure is formed inside the hard carbon material, which helps to improve the material's sodium storage performance and cycle stability. Polyamic acid acts as a pore former and a closed-cell agent on bio-based materials to form a rich closed-cell structure. The closed-cell structure provides a rich sodium storage site for hard carbon materials, giving them a high reversible capacity. This helps to improve the energy density and endurance of sodium-ion batteries. The closed-cell structure helps to reduce the volume change of the material during the charge and discharge process, thereby improving the material's cycle stability. The closed-cell structure is conducive to the penetration of the electrolyte and the rapid transmission of ions, thereby improving the material's rate performance.

[0035] In the technical solution of the present invention, the biomass carbon source is first cleaned. The three-dimensional network structure of the biomass carbon source molecules themselves may cause some impurities in the biomass carbon source that may interfere with the carbonization process. The impurities in the biomass carbon source can be removed from the biomass carbon source raw material through cleaning to improve the purity of the reactants.

[0036] In some embodiments, the biomass carbon source is dissolved in deionized water and an acidic solution in turn using a funnel for washing, and the process is repeated three times. A glass rod is used to stir the biomass carbon source to assist in dissolving it in deionized water or an acidic solution for thorough washing. After washing, the biomass carbon source is dried in an oven. By washing with water, soluble impurities and ash in the biomass carbon source can be preliminarily removed to improve purity; acid washing can further remove inorganic impurities in the biomass carbon source and improve the purity and stability of the resulting biomass hard carbon precursor. In addition, acid washing can change the functional group composition on the surface of the biomass carbon source, increase the number of oxygen-containing functional groups, improve the surface chemical properties of the hard carbon material, and improve the compatibility and stability of the hard carbon material with other materials.

[0037] In some embodiments, the ball milling process is performed at a rotation speed of 300 to 500 r / min and a time of 120 to 240 min. Within the range of the rotation speed and time of the ball milling process, the precursor powder and the polyamic acid can be fully mixed.

[0038] In some embodiments, the polyamic acid includes at least one of aliphatic polyamic acid, furan-based polyamic acid and aromatic polyamic acid; the biomass hard carbon precursor powder is mixed with the polyamic acid powder in a mass ratio of 1:(0.1-0.5). By controlling the amount of polyamic acid, the morphology and proportion of the pores and channels of the biomass hard carbon material can be controlled, and then the size, morphology and structure of the microscopic pores of the material can be controlled. Taking into account the electrochemical properties, structural stability and preparation cost of the prepared hard carbon material, a more ideal effect can be obtained when the mass ratio of the biomass hard carbon precursor to the polyamic acid is within the above range. As an example, the mass ratio of the biomass hard carbon precursor to the furan-based polyamic acid can be 1:0.3.

[0039] In some embodiments, the temperature T1 of the first carbonization treatment is 400-800°C, and the time is 2-4 hours. When the first carbonization treatment is at the aforementioned treatment time and treatment temperature, it helps to release the hydrogen atoms in the biomass hard carbon precursor 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. As an example, T1 can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C.

[0040] In some embodiments, the temperature T2 of the second carbonization treatment is 1100-1500°C, and the time is 2-4 hours. When the second carbonization treatment is at the aforementioned treatment time and treatment temperature, the microstructure of the composite material can be further adjusted and optimized by carbonization to obtain a hard carbon material with a suitable interlayer spacing. As an example, T2 can be 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C or 1500°C.

[0041] In some embodiments, the heating rates of the first carbonization treatment and the second carbonization treatment are independently 2 to 10°C / min. During the carbonization treatment, when the heating rate is within the aforementioned range, the carbonized polymer, i.e., the biomass hard carbon precursor used in the present invention, can reduce the degree of side reactions such as oxidation reaction and decomposition reaction that may occur during its carbonization process.

[0042] In some embodiments, the first protective atmosphere and the second protective atmosphere each independently include N 2 and inert gas; and / or, the carbonization treatment equipment is a high temperature tube furnace.

[0043] In a second aspect of the present invention, the present invention provides a negative electrode active material, comprising the hard carbon material.

[0044] In a third aspect of the present invention, the present invention provides a sodium ion battery, comprising the sodium ion battery negative electrode active material.

[0045] In some embodiments, after the hard carbon material is ground and screened, it is mixed and ground with carbon black and a binder in a mass ratio of 90:5:5, wherein 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.

[0046] The scheme of the present invention 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.

[0047] The preparation method of poly (pyromellitic anhydride-furan diamine) amic acid powder used in the following examples is as follows: Under nitrogen protection, 2,5-furan diamine is dissolved in pre-cooled (0-5°C) N-methylpyrrolidone (NMP) solvent and stirred until completely dissolved. Pyromellitic anhydride (PMDA) powder is added in batches, and the molar ratio is controlled to be diamine: dianhydride = 1: 1.02-1.03, and the reaction temperature is maintained at ≤ 5°C to avoid gelation caused by intense heat release. Stirring is continued for 12-24 hours until a viscous polyamic acid (PAA) solution is formed. The reaction solution is slowly dripped into a deionized water / methanol mixture (volume ratio 1: 1) to precipitate a white flocculent precipitate. After filtration, it is washed with methanol and deionized water in turn to remove residual solvents and oligomers. Vacuum drying (80°C, 12 hours) and grinding to obtain poly (pyromellitic anhydride-furan diamine) amic acid powder.

[0048] Example 1

[0049] This embodiment prepares high-capacity biomass hard carbon material according to the following steps:

[0050] S1. Pretreatment: 20 g of biomass carbon source (bamboo powder) was dissolved in water and 1 mol / L hydrochloric acid solution for washing, and the mixture was repeated three times. The mixture was stirred with a glass rod. After washing, the mixture was dried in an oven at 80° C. for 24 h to obtain a biomass hard carbon precursor powder.

[0051] S2, ball milling and mixing: the biomass hard carbon precursor powder of step S1 and the poly (pyromellitic anhydride-furan diamine) amic acid powder are mixed in a mass ratio of 1:0.3, weighed, and ball milled at a speed of 300 r / min for 120 min to obtain a mixed powder.

[0052] S3, pre-carbonization: put the mixed powder obtained in step S2 into a tube furnace at N 2 The first carbonization treatment was carried out in the atmosphere at a carbonization temperature of 600°C, a heating rate of 5°C / min, and a time of 2h to obtain a composite material, the SEM image of which is shown in FIG. Figure 1 shown.

[0053] S4, post-processing: put the composite material obtained in step S3 into a tube furnace and heat it at N 2 The second carbonization treatment was carried out in the atmosphere at a carbonization temperature of 1400°C, a heating rate of 5°C / min, and a time of 2h to obtain a hard carbon material, the SEM image of which is shown in Figure 2 shown.

[0054] Example 2

[0055] In this embodiment, a high-capacity biomass hard carbon material is prepared in the same manner as in Embodiment 1, with the only difference being that the temperature of the second carbonization treatment is 1300°C.

[0056] Example 3

[0057] In this embodiment, a high-capacity biomass hard carbon material is prepared in the same manner as in Embodiment 1, with the only difference being that the temperature of the second carbonization treatment is 1500°C.

[0058] Example 4

[0059] In this embodiment, a high-capacity biomass hard carbon material is prepared in the same manner as in Embodiment 1, with the only difference being that, during the acid treatment in step S1, the acid solution used is a 4 mol / L hydrochloric acid solution.

[0060] Example 5

[0061] In this embodiment, a high-capacity biomass hard carbon material is prepared by the same method as in Embodiment 1, except that the ball milling time in step S2 is 4 hours.

[0062] Example 6

[0063] In this embodiment, a high-capacity biomass hard carbon material is prepared by the same method as in Embodiment 1, except that in step S2, the mass ratio of the biomass hard carbon precursor powder to the poly(pyromellitic anhydride-furan diamine) amic acid powder is 1:0.6.

[0064] Comparative Example 1

[0065] This comparative example prepares the biomass hard carbon material according to the following steps:

[0066] S1. Pretreatment: 20 g of biomass carbon source (bamboo powder) was dissolved in water and 1 mol / L hydrochloric acid solution for washing, and the mixture was repeated three times. The mixture was stirred with a glass rod. After washing, the mixture was dried in an oven at 80° C. for 24 h to obtain a biomass hard carbon precursor powder.

[0067] S2, pre-carbonization: put the biomass hard carbon precursor powder obtained in step S1 into a tube furnace at N 2 The first carbonization treatment was carried out in an atmosphere at a carbonization temperature of 600° C., a heating rate of 5° C. / min, and a time of 2 h to obtain a composite material.

[0068] S3, post-processing: put the composite material obtained in step S2 into a tube furnace and heat it at N 2 The second carbonization treatment was carried out in the atmosphere with a carbonization temperature of 1400°C, a heating rate of 5°C / min and a time of 2h to obtain a hard carbon material.

[0069] Comparative Example 2

[0070] This comparative example prepares the biomass hard carbon material according to the following steps:

[0071] S1. Pretreatment: 20 g of biomass carbon source (bamboo powder) was dissolved in water and 1 mol / L hydrochloric acid solution for washing, and the mixture was repeated three times. The mixture was stirred with a glass rod. After washing, the mixture was dried in an oven at 80° C. for 24 h to obtain a biomass hard carbon precursor powder.

[0072] S2, ball milling and mixing: the biomass hard carbon precursor powder of step S1 and the poly (pyromellitic anhydride-furan diamine) amic acid powder are mixed in a mass ratio of 1:0.3, and ball milled at a speed of 300 r / min for 120 min to obtain a mixed powder.

[0073] S3, carbonization: put the mixed powder obtained in step S2 into a tube furnace at N 2 Carbonization was carried out in an atmosphere at a carbonization temperature of 1400°C, a heating rate of 5°C / min, and a time of 2h to obtain a hard carbon material.

[0074] Comparative Example 3

[0075] This embodiment prepares high-capacity biomass hard carbon material according to the following steps:

[0076] S1. Pretreatment: 20 g of biomass carbon source (bamboo powder) was dissolved in water and 1 mol / L hydrochloric acid solution for washing, and the mixture was repeated three times. The mixture was stirred with a glass rod. After washing, the mixture was dried in an oven at 80° C. for 24 h to obtain a biomass hard carbon precursor powder.

[0077] S2, ball milling and mixing: the biomass hard carbon precursor powder of step S1 and the poly (pyromellitic anhydride-furan diamine) amic acid powder are mixed in a mass ratio of 1:0.3, weighed, and ball milled at a speed of 300 r / min for 120 min to obtain a mixed powder.

[0078] S3, pre-carbonization: put the mixed powder obtained in step S2 into a tube furnace at N 2 The first carbonization treatment was carried out in the atmosphere at a carbonization temperature of 600°C, a heating rate of 5°C / min, and a time of 2h to obtain a carbon material.

[0079] The hard carbon materials prepared in the above embodiments and comparative examples are used as negative electrode active materials to assemble button-type batteries, and the specific steps are as follows:

[0080] The hard carbon material was mixed with carbon black, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of 90:5:2.5:2.5, and mixed evenly in a mortar with deionized water as a dispersant to form a slurry, which was evenly coated on a copper foil with a coater, placed in a vacuum drying oven at 80°C for 12 hours, and then prepared into a negative electrode sheet with a diameter of 14 mm with a sheet puncher. A glass fiber disc was used as a diaphragm, a sodium metal sheet was used as a counter electrode and a reference electrode, and the electrolyte was sodium hexafluorophosphate dissolved in diethylene glycol dimethyl ether (concentration of 1 mol / L). The sodium ion battery was assembled in a glove box filled with high-purity argon according to the structure of a CR2032 standard button cell.

[0081] The sodium ion batteries assembled with the materials prepared in the embodiments and comparative examples were charged and discharged on a battery test platform at a current density of 50 mA / g. The results are shown in Table 1.

[0082] Table 1

[0083] <![CDATA[Reversible specific capacity / mAh·g ～1 > First coulombic efficiency / % <![CDATA[Specific surface area m 2 / g]]> Example 1 385 93 4.8 Example 2 351 89 7.1 Example 3 332 87 5.3 Example 4 324 80 21.4 Example 5 307 83 9.3 Example 6 313 86 14.7 Comparative Example 1 212 82 102.1 Comparative Example 2 327 88 30.8 Comparative Example 3 127 30 417.0

[0084] See also Figure 1 The carbon material that has only undergone the first carbonization treatment but not the second carbonization treatment has irregular pores with uneven pore sizes ranging from 1 to 5 μm. Figure 2 The hard carbon material obtained after the second carbonization treatment has an irregular shape, uneven particle size of 2 to 10 μm, a relatively smooth surface, and moderate pores. By comparing Example 1 with Comparative Example 3 in Table 1, it can be clearly found that the specific surface area of ​​the activated carbon material after high-temperature carbonization has decreased significantly, which is inferred to be the collapse of the pores of the carbon material to form a closed-cell structure.

[0085] The XRD pattern of the hard carbon material in Example 1 is as follows: Figure 3 As shown in the figure, it can be seen 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 microcrystals of this hard carbon material have a high degree of disorder and a large interlayer spacing, which is conducive to the deintercalation of sodium ions.

[0086] The charge and discharge curve of the sodium ion battery assembled from the hard carbon material in Example 1 is as follows: Figure 4 As shown in the figure, it can be seen that the assembled sodium ion battery has a high specific capacity of 385 mAh g ～1 , the first charge and discharge efficiency is 93%.

[0087] 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.

[0088] It should be noted that the present invention 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 the same effect within the scope of the technical solution of the present invention 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 invention.

Claims

1. A method for preparing a high-capacity biomass hard carbon material, characterized in that: The following steps are involved: S1. Pretreatment: dissolving the biomass carbon source in water and an acid solution in sequence for washing, and then drying to obtain a biomass hard carbon precursor powder; S2, ball milling and mixing: ball milling the biomass hard carbon precursor powder and the polyamic acid powder to uniformly mix to obtain a mixed powder; S3, pre-carbonization: performing a first carbonization treatment on the mixed powder in a first protective atmosphere to obtain a composite material; S4, post-processing: in a second protective atmosphere, the composite material obtained in step S3 is further subjected to a second carbonization treatment to obtain a hard carbon material.

2. The method for preparing a high-capacity biomass hard carbon material according to claim 1, characterized in that: In step S1: the acidic solution includes at least one of a hydrochloric acid solution and a sulfuric acid solution, the concentration of the acidic solution is 0.5 to 2 mol / L, and the biomass carbon source is treated in the acidic solution for 2 to 10 hours; the drying temperature is 60 to 100° C., and the drying time is 20 to 30 hours.

3. The method for preparing a high-capacity biomass hard carbon material according to claim 1, characterized in that: In step S2: the polyamic acid includes at least one of aliphatic polyamic acid, furan-based polyamic acid and aromatic polyamic acid; the biomass hard carbon precursor powder and the polyamic acid powder are mixed at a mass ratio of 1:0.1 to 0.

5.

4. The method for preparing a high-capacity biomass hard carbon material according to claim 1, characterized in that: In step S2: the rotation speed of the ball mill is 300-500 r / min, and the time is 120-240 min.

5. The method for preparing a high-capacity biomass hard carbon material according to claim 1, characterized in that: In step S3: the temperature of the first carbonization treatment is 400-800°C, the time is 2-4h, and the heating rate is 2-10°C / min.

6. The method for preparing a high-capacity biomass hard carbon material according to claim 1, characterized in that: In step S4: the temperature of the second carbonization treatment is 1100-1500°C, the time is 2-4h, and the heating rate is 2-10°C / min.

7. The method for preparing a high-capacity biomass hard carbon material according to claim 1, characterized in that: The biomass carbon source includes at least one of coconut shell, starch, bamboo powder, straw, walnut shell, potato and wheat.

8. A high-capacity biomass hard carbon material obtained by the preparation method according to any one of claims 1 to 7.

9. A negative electrode active material, characterized in that: Comprising the hard carbon material as claimed in claim 8.

10. A sodium ion battery, characterized in that: Comprising the negative electrode active material according to claim 9.

Images