A bamboo-based hard carbon sodium-ion battery negative electrode material and a preparation method thereof

Abstract

The application relates to the technical field of electrochemical energy storage materials, and particularly discloses a bamboo-based hard carbon sodium ion battery negative electrode material and a preparation method thereof. The preparation method comprises the following steps: taking natural bamboo as a carbon source precursor, and sequentially performing raw material pretreatment, mixed acid system purification and impurity removal, modified impregnation liquid vacuum crosslinking modification, two-section inert atmosphere carbonization and organic-inorganic composite passivation coating treatment to obtain a bamboo-based hard carbon negative electrode material. The application solves the technical defects that the existing bamboo-based hard carbon material has low first coulomb efficiency, poor cycle stability, and difficult-to-achieve coexistence of sodium storage capacity and first efficiency, and the preparation process is controllable, green and low in cost; the graphite interlayer spacing, pore structure and surface state of the hard carbon material can be accurately controlled; the obtained material has excellent electrochemical performance and is suitable for the field of large-scale energy storage of sodium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage materials, and more specifically, to a hard carbon sodium-ion battery anode material based on bamboo and its preparation method. Background Technology

[0002] Sodium-ion batteries are considered an important supplement to lithium-ion batteries in the field of large-scale energy storage due to the abundance, wide distribution, and low cost of sodium resources. However, the graphite anode materials used in traditional lithium-ion batteries have small interlayer spacing, making it difficult to effectively achieve reversible insertion and extraction of sodium ions, resulting in extremely low sodium storage capacity and making them unsuitable for direct application in sodium-ion batteries. Hard carbon materials, with their large graphite interlayer spacing, abundant nanoporous structure, and good electronic conductivity, can provide ample storage space and transport pathways for sodium ions, making them a current research hotspot for sodium-ion battery anode materials.

[0003] Currently, industrially produced hard carbon materials mainly originate from fossil raw materials such as petroleum coke, asphalt, and phenolic resin, which presents significant challenges including high raw material costs, non-renewable resources, and large carbon emissions during the preparation process. In recent years, the preparation of hard carbon materials using biomass as a precursor has attracted widespread attention due to its advantages such as renewability, environmental friendliness, and tunable structure. Bamboo, as a fast-growing and widely distributed natural polymer material, is rich in cellulose, hemicellulose, and lignin, possessing a natural hierarchical porous structure, and theoretically can serve as an ideal precursor for preparing hard carbon anode materials. However, existing technologies that directly carbonize bamboo often suffer from problems such as excessive specific surface area, numerous surface defects, and low initial coulombic efficiency. An excessively high specific surface area leads to the formation of excessive solid electrolyte interfacial films during the initial charge-discharge process, causing irreversible capacity loss; while excessive surface defects exacerbate side reactions in the electrolyte, affecting the material's cycle stability. Therefore, this invention provides a bamboo-based hard carbon sodium-ion battery anode material and its preparation method to address the aforementioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a hard carbon sodium-ion battery anode material based on bamboo and its preparation method. This invention solves the technical defects of existing bamboo-based hard carbon materials, such as low initial coulombic efficiency, poor cycle stability, and difficulty in balancing sodium storage capacity and initial efficiency. The preparation process is controllable, green and low-cost, and can precisely control the graphite interlayer spacing, pore structure and surface state of the hard carbon material. The resulting material has excellent electrochemical performance and is suitable for large-scale sodium-ion battery energy storage.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a hard carbon sodium-ion battery anode material based on bamboo, employing the following technical solution:

[0006] A method for preparing a hard carbon sodium-ion battery anode material based on bamboo includes the following steps:

[0007] S1. Remove the outer skin and nodes from 3-5 year old moso bamboo and cut it into 1-2cm pieces. 3 The lumpy material was ultrasonically cleaned with deionized water for 30-40 minutes, then dried at 60-70℃ to constant weight. The resulting material was then ball-milled, pulverized, and sieved to collect particles with a particle size D. 50 Prepare bamboo powder with a particle size of 20-40μm;

[0008] S2. The bamboo powder obtained in step S1 is immersed in a mixed acid solution prepared by mixing 5-8%wt dilute hydrochloric acid and 2-4%wt oxalic acid in a volume ratio of (5-7):1 at a solid-liquid ratio of 1g: (8-12)ml. The mixture is stirred at 80-90℃ and 300-350rpm for 2-3 hours, then filtered under reduced pressure, washed with water until neutral, and dried under vacuum to obtain pure bamboo powder.

[0009] S3. Take 20-25 parts of pure bamboo powder and place them in a vacuum mixer. Start the mixer and add 40-45 parts of modified impregnation liquid at one time. Mix initially to form a slurry. Continue stirring under vacuum for 15-25 minutes. After the vacuum is released, raise the temperature to 85-95℃ and continue stirring and reacting at 300-400 rpm under normal pressure for 2-3 hours. Then, vacuum dry to obtain the modified bamboo powder precursor.

[0010] S4. The modified bamboo powder precursor is placed in a tube furnace and high-purity argon is introduced. The temperature is raised to 300-400℃ at 2-5℃ / min and held for 2-2.5h to complete the pre-carbonization. Then, it is heated to 1200-1400℃ at 3-5℃ / min and held for 3-5h for high-temperature carbonization. After completion, it is naturally cooled to room temperature to obtain primary hard carbon powder.

[0011] S5. Disperse 10-15 parts of primary hard carbon powder ultrasonically in a mixed solvent of anhydrous ethanol and deionized water with a volume ratio of (1-3):1 for 30-40 minutes to obtain dispersion A; dissolve 0.8-1.5 parts of dopamine hydrochloride in 3-5 parts of deionized water to obtain solution B; mix 10-15 parts of tris(hydroxymethyl)aminomethane buffer solution with pH 8.2-8.5 with 0.3-0.6 parts of tetraethyl orthosilicate and pre-hydrolyze for 5-8 minutes to obtain solution C for later use.

[0012] S6. In an ice-water bath at 250-350 rpm, first add solution B dropwise to dispersion A at 1-3 ml / min, then add solution C dropwise to the above mixture. After the addition is complete, stir the mixture at 300-400 rpm in the dark at room temperature for 12-16 h. After centrifugation, washing, and vacuum drying, heat the mixture in a tube furnace at 600-650℃ under high-purity argon at 3-4℃ / min for 1-2 h. Then, ball mill the product at 200-300 rpm for 0.5-1 h, and then pass it through a 300-mesh standard sieve to obtain the bamboo-based hard carbon sodium-ion battery anode material.

[0013] Preferably, the bamboo used in step S1 is 3-5 year old bamboo, and the size of the block is 1-2 cm. 3 The ultrasonic cleaning time is 30-40 minutes, the drying temperature is 60-70℃, and the particle size D of the resulting bamboo powder is... 50 It is 20-40μm.

[0014] Preferably, in step S2, the mixed acid solution is prepared by dilute hydrochloric acid and oxalic acid, the solid-liquid ratio of bamboo powder to the mixed acid solution is 1g:(8-12)ml, the stirring reaction temperature is 80-90℃, the stirring speed is 300-350rpm, and the reaction time is 2-3h.

[0015] Preferably, in step S3, the amount of pure bamboo powder is 20-25 parts and the amount of modified impregnation solution is 40-45 parts; the modified impregnation solution is prepared by dissolving pentaerythritol, citric acid and phytic acid in deionized water.

[0016] Preferably, the modified impregnation solution is prepared by dissolving 3-5 parts pentaerythritol, 2-4 parts citric acid and 1-3 parts phytic acid in 25-30 parts deionized water, stirring at 70-80℃ and 400-450rpm until completely dissolved, to obtain a clear and transparent impregnation solution, which is then kept warm for later use.

[0017] Preferably, in step S4, the pre-carbonization temperature is 300-400℃, the holding time is 2-2.5h, and the heating rate is 2-5℃ / min; the high-temperature carbonization temperature is 1200-1400℃, the holding time is 3-5h, and the heating rate is 3-5℃ / min.

[0018] Preferably, in step S5, the primary hard carbon powder is 10-15 parts, the mixed solvent is 70-80 parts, the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is (1-3):1; dopamine hydrochloride is 0.8-1.5 parts, tris(hydroxymethyl)aminomethane buffer is 10-15 parts, and tetraethyl orthosilicate is 0.3-0.6 parts.

[0019] Preferably, in step S6, the stirring speed during the dropping process is 250-350 rpm, the dropping rate of solution B is 1-3 ml / min, the stirring reaction time at room temperature in the dark is 12-16 h, the heat treatment temperature is 600-650℃, the holding time is 1-2 h, and the heating rate is 3-4℃ / min.

[0020] A second aspect of the present invention provides a bamboo-based hard carbon sodium-ion battery anode material prepared by any of the above-mentioned preferred preparation methods.

[0021] Preferably, the graphite interlayer spacing of the bamboo-based hard carbon sodium-ion battery anode material is 0.38-0.40 nm, the reversible capacity at a current density of 0.1 A / g is ≥320 mAh / g, and the initial coulombic efficiency is ≥87%.

[0022] In summary, the present invention has the following beneficial effects:

[0023] 1. This invention involves deep purification of natural bamboo powder using a mixed acid system composed of dilute hydrochloric acid and oxalic acid. This effectively removes metallic ash impurities in the precursor that easily induce catalytic graphitization. Vacuum crosslinking modification is then performed using a multi-component modified impregnation solution composed of pentaerythritol, citric acid, and phytic acid. Combined with a two-stage programmed temperature carbonization process, a hard carbon precursor system with a stable framework and uniform heteroatom distribution is formed. This process effectively solves the problems of graphite interlayer shrinkage and severe interfacial side reactions caused by ash residue in existing biomass hard carbon technologies. By leveraging the deep chelating effect of the mixed acid and the molecular-level crosslinking support effect of the modified components, precise expansion of the graphite interlayer spacing and effective directional control of the microporous structure of the hard carbon material are achieved, significantly improving the sodium ion storage capacity and diffusion kinetics. Simultaneously, in-situ phosphorus doping enhances the chemical stability of the carbon framework, effectively preventing microstructural collapse during high-temperature carbonization, ensuring the structural integrity of the material during charge and discharge, and improving the material's consistency and economy.

[0024] 2. The organic-inorganic composite passivation coating of this invention is formed by in-situ self-polymerization of dopamine hydrochloride in a weakly alkaline buffer system, and compounded with silica components generated by the hydrolysis of tetraethyl orthosilicate. This coating system, through the physical shielding and interface strengthening effects of the nitrogen-doped carbon layer provided by polydopamine and silica, forms a multi-component synergistic passivation system, which can effectively suppress excessive electrolyte decomposition caused by residual open pores on the hard carbon surface. Specifically, the nitrogen-containing functional groups generated by the pyrolysis of polydopamine optimize the surface charge distribution and induce the formation of a thin and dense solid electrolyte interface film. The silica component significantly improves the material's exclusion capacity for co-intercalation with macromolecular solvents by enhancing the mechanical modulus and chemical resistance of the artificial interface layer. The synergistic effect of the compounded components ensures efficient sodium ion penetration while significantly improving the initial coulombic efficiency and significantly reducing irreversible capacity loss, providing a key guarantee for the long-term cycling stability of hard carbon materials in large-scale energy storage applications. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used, unless otherwise specified, were all purchased from conventional biochemical reagent stores. All quantitative experiments in the following examples were performed in triplicate, and the data are the average of the three replicates or the average ± standard deviation.

[0027] SuperP, purchased from Tianjin Yiborui Chemical Co., Ltd., CAS No. 1333-86-4;

[0028] Example 1

[0029] This embodiment provides a method for preparing a hard carbon sodium-ion battery anode material based on bamboo, using the following technical solution:

[0030] S1. Remove the outer skin and nodes from 3-year-old bamboo and cut it into 2cm pieces. 3 The lumpy material was ultrasonically cleaned with deionized water for 30 minutes, dried at 60℃ to constant weight, and then ball-milled, pulverized, and sieved to collect particles with a particle size D. 50 Prepare 40μm bamboo powder for later use;

[0031] S2. The bamboo powder obtained in step S1 is immersed in a mixed acid solution prepared by mixing 5%wt dilute hydrochloric acid and 2%wt oxalic acid in a volume ratio of 5:1 at a solid-liquid ratio of 1g:8ml. After stirring and reacting at 80℃ and 300rpm for 3h, the mixture is filtered under reduced pressure, washed with water until neutral, and then dried under vacuum to obtain pure bamboo powder.

[0032] S3. Place 20 parts of pure bamboo powder in a vacuum mixer, start the mixer and add 40 parts of modified impregnation liquid at once to initially mix and form a slurry. Continue stirring under vacuum for 15 minutes. After releasing the vacuum, raise the temperature to 85°C and continue stirring at 300 rpm under normal pressure for 3 hours. Then, vacuum dry to obtain the modified bamboo powder precursor. The preparation process of the modified impregnation liquid is as follows: dissolve 3 parts of pentaerythritol, 2 parts of citric acid and 1 part of phytic acid in 25 parts of deionized water and stir at 70°C and 400 rpm until completely dissolved to obtain a clear and transparent impregnation liquid. Keep it warm for later use.

[0033] S4. The modified bamboo powder precursor is placed in a tube furnace and high-purity argon is introduced. The temperature is raised to 300℃ at 2℃ / min and held for 2.5h to complete the pre-carbonization. Then, it is heated to 1200℃ at 3℃ / min and held for 5h to carry out high-temperature carbonization. After completion, it is naturally cooled to room temperature to obtain primary hard carbon powder.

[0034] S5. Disperse 10 parts of primary hard carbon powder ultrasonically in a mixed solvent of 70 parts of anhydrous ethanol and deionized water at a volume ratio of 1:1 for 30 min to obtain dispersion A; dissolve 0.8 parts of dopamine hydrochloride in 3 parts of deionized water to obtain solution B; mix 10 parts of tris(hydroxymethyl)aminomethane buffer solution with pH 8.2 with 0.3 parts of tetraethyl orthosilicate and pre-hydrolyze for 8 min to obtain solution C for later use.

[0035] S6. Under ice-water bath and 250 rpm, solution B is first added dropwise to dispersion A at 1 ml / min, followed by solution C being added dropwise to the above mixture. After the addition is complete, the mixture is stirred at 300 rpm in the dark at room temperature for 16 h. After centrifugation, washing, and vacuum drying, the mixture is heat-treated in a tube furnace at 600 °C under high-purity argon at 3 °C / min for 2 h. The product is then ball-milled at 200 rpm for 1 h and then passed through a 300-mesh standard sieve to obtain the bamboo-based hard carbon sodium-ion battery anode material.

[0036] Example 2

[0037] This embodiment provides a method for preparing a hard carbon sodium-ion battery anode material based on bamboo, using the following technical solution:

[0038] S1. Remove the outer skin and nodes from 4-year-old bamboo and cut it into 1cm pieces. 3 The lumpy material was ultrasonically cleaned with deionized water for 35 minutes, dried at 65°C to constant weight, and then ball-milled, pulverized, and sieved to collect particles with a particle size D. 50Prepare 30μm bamboo powder for later use;

[0039] S2. The bamboo powder obtained in step S1 is immersed in a mixed acid solution prepared by mixing 6%wt dilute hydrochloric acid and 3%wt oxalic acid in a volume ratio of 6:1 at a solid-liquid ratio of 1g:9ml. The mixture is stirred at 85℃ and 310rpm for 2.8h, then filtered under reduced pressure, washed with water until neutral, and dried under vacuum to obtain pure bamboo powder.

[0040] S3. Place 22 parts of pure bamboo powder in a vacuum mixer, start the mixer and add 42 parts of modified impregnation liquid at once to initially mix and form a slurry. Continue stirring under vacuum for 24 minutes. After the vacuum is released, raise the temperature to 88°C and continue stirring at 320 rpm under normal pressure for 2.8 hours. Then vacuum dry to obtain the modified bamboo powder precursor. The preparation process of the modified impregnation liquid is as follows: dissolve 4 parts of pentaerythritol, 3 parts of citric acid and 2 parts of phytic acid in 28 parts of deionized water, stir at 72°C and 410 rpm until completely dissolved to obtain a clear and transparent impregnation liquid, and keep it warm for later use.

[0041] S4. The modified bamboo powder precursor is placed in a tube furnace and high-purity argon is introduced. The temperature is raised to 320℃ at 3℃ / min and held for 2.4h to complete the pre-carbonization. Then, it is heated to 1300℃ at 4℃ / min and held for 4.8h for high-temperature carbonization. After completion, it is naturally cooled to room temperature to obtain primary hard carbon powder.

[0042] S5. Disperse 12 parts of primary hard carbon powder ultrasonically in a mixed solvent of 72 parts of anhydrous ethanol and deionized water at a volume ratio of 2:1 for 32 min to obtain dispersion A; dissolve 0.9 parts of dopamine hydrochloride in 4 parts of deionized water to obtain solution B; mix 12 parts of tris(hydroxymethyl)aminomethane buffer solution with pH 8.3 with 0.4 parts of tetraethyl orthosilicate and pre-hydrolyze for 7 min to obtain solution C for later use.

[0043] S6. Under ice-water bath and 280 rpm, solution B is first added dropwise to dispersion A at 2 ml / min, followed by solution C. After the addition is complete, the mixture is stirred at 320 rpm in the dark at room temperature for 15 h. After centrifugation, washing, and vacuum drying, the mixture is heat-treated in a tube furnace at 620 °C under high-purity argon at 3.5 °C / min for 1.8 h. The product is then ball-milled at 220 rpm for 0.8 h and then passed through a 300-mesh standard sieve to obtain the bamboo-based hard carbon sodium-ion battery anode material.

[0044] Example 3

[0045] This embodiment provides a method for preparing a hard carbon sodium-ion battery anode material based on bamboo, using the following technical solution:

[0046] S1. Remove the outer skin and nodes from 5-year-old bamboo and cut it into 2cm pieces. 3The lumpy material was ultrasonically cleaned with deionized water for 40 minutes, dried at 70℃ to constant weight, and then ball-milled, pulverized, and sieved to collect particles with a particle size D. 50 Prepare 20μm bamboo powder for later use;

[0047] S2. The bamboo powder obtained in step S1 is immersed in a mixed acid solution prepared by mixing 8%wt dilute hydrochloric acid and 4%wt oxalic acid in a volume ratio of 7:1 at a solid-liquid ratio of 1g:12ml. After stirring and reacting at 90℃ and 350rpm for 2h, the mixture is filtered under reduced pressure, washed with water until neutral, and then dried under vacuum to obtain pure bamboo powder.

[0048] S3. Place 25 parts of pure bamboo powder in a vacuum mixer, start the mixer and add 45 parts of modified impregnation liquid at once to initially mix and form a slurry. Continue stirring under vacuum for 15 minutes. After releasing the vacuum, raise the temperature to 95°C and continue stirring at 400 rpm under normal pressure for 2 hours. Then vacuum dry to obtain the modified bamboo powder precursor. The preparation process of the modified impregnation liquid is as follows: dissolve 5 parts of pentaerythritol, 4 parts of citric acid and 3 parts of phytic acid in 30 parts of deionized water, and stir at 80°C and 450 rpm until completely dissolved to obtain a clear and transparent impregnation liquid. Keep it warm for later use.

[0049] S4. The modified bamboo powder precursor is placed in a tube furnace and high-purity argon is introduced. The temperature is raised to 400℃ at 5℃ / min and held for 2 hours to complete the pre-carbonization. Then, it is heated to 1400℃ at 5℃ / min and held for 3 hours for high-temperature carbonization. After completion, it is naturally cooled to room temperature to obtain primary hard carbon powder.

[0050] S5. Disperse 15 parts of primary hard carbon powder ultrasonically in a mixed solvent of 80 parts of anhydrous ethanol and deionized water at a volume ratio of 3:1 for 30 min to obtain dispersion A; dissolve 1.5 parts of dopamine hydrochloride in 5 parts of deionized water to obtain solution B; mix 15 parts of tris(hydroxymethyl)aminomethane buffer solution with pH 8.5 with 0.6 parts of tetraethyl orthosilicate and pre-hydrolyze for 5 min to obtain solution C for later use.

[0051] S6. Under ice-water bath and 350 rpm, solution B is first added dropwise to dispersion A at 3 ml / min, followed by solution C. After the addition is complete, the mixture is stirred at 400 rpm in the dark at room temperature for 12 h. After centrifugation, washing, and vacuum drying, the mixture is heat-treated in a tube furnace at 650 °C under high-purity argon at 4 °C / min for 1 h. The product is then ball-milled at 300 rpm for 0.5 h and then passed through a 300-mesh standard sieve to obtain the bamboo-based hard carbon sodium-ion battery anode material.

[0052] Example 4

[0053] This embodiment provides a method for preparing a hard carbon sodium-ion battery anode material based on bamboo, using the following technical solution:

[0054] S1. Remove the outer skin and nodes from 5-year-old bamboo and cut it into 2cm pieces. 3 The lumpy material was ultrasonically cleaned with deionized water for 40 minutes, dried at 70℃ to constant weight, and then ball-milled, pulverized, and sieved to collect particles with a particle size D. 50 Prepare 25μm bamboo powder for later use;

[0055] S2. The bamboo powder obtained in step S1 is immersed in a mixed acid solution prepared by mixing 8%wt dilute hydrochloric acid and 4%wt oxalic acid in a volume ratio of 6:1 at a solid-liquid ratio of 1g:10ml. The mixture is stirred at 90℃ and 350rpm for 2.4h, then filtered under reduced pressure, washed with water until neutral, and dried under vacuum to obtain pure bamboo powder.

[0056] S3. Place 25 parts of pure bamboo powder in a vacuum mixer, start the mixer and add 45 parts of modified impregnation liquid at once to initially mix and form a slurry. Continue stirring under vacuum for 20 minutes. After releasing the vacuum, raise the temperature to 90°C and continue stirring at 400 rpm under normal pressure for 2.5 hours. Then vacuum dry to obtain the modified bamboo powder precursor. The preparation process of the modified impregnation liquid is as follows: dissolve 5 parts of pentaerythritol, 4 parts of citric acid and 3 parts of phytic acid in 30 parts of deionized water, stir at 80°C and 420 rpm until completely dissolved to obtain a clear and transparent impregnation liquid, and keep it warm for later use.

[0057] S4. The modified bamboo powder precursor is placed in a tube furnace and high-purity argon is introduced. The temperature is raised to 400℃ at 3℃ / min and held at 4℃ / min for 2 hours to complete the pre-carbonization. Then, the temperature is raised to 1200℃ at 4℃ / min and held at 4℃ / min for 3.2 hours to carry out high-temperature carbonization. After completion, the raw material is naturally cooled to room temperature to obtain primary hard carbon powder.

[0058] S5. Disperse 15 parts of primary hard carbon powder ultrasonically in a mixed solvent of 70 parts of anhydrous ethanol and deionized water at a volume ratio of 3:1 for 40 min to obtain dispersion A; dissolve 1.5 parts of dopamine hydrochloride in 5 parts of deionized water to obtain solution B; mix 15 parts of tris(hydroxymethyl)aminomethane buffer solution with pH 8.5 with 0.6 parts of tetraethyl orthosilicate and pre-hydrolyze for 8 min to obtain solution C for later use.

[0059] S6. Under ice-water bath and 280 rpm, solution B is first added dropwise to dispersion A at 2 ml / min, and then solution C is added dropwise to the above mixture. After the addition is complete, the mixture is stirred at 300 rpm in the dark at room temperature for 12 h. After centrifugation, washing, and vacuum drying, the mixture is heat-treated in a tube furnace at 650 °C under high-purity argon at 4 °C / min for 1.2 h. The product is then ball-milled at 300 rpm for 0.8 h and then passed through a 300-mesh standard sieve to obtain the bamboo-based hard carbon sodium-ion battery anode material.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 4 is that the multi-component in-situ impregnation modification treatment in step S3 is omitted, that is, the pure bamboo powder obtained in step S2 is directly used as a precursor for carbonization treatment in step S4, and other conditions are the same as in Example 4.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 4 is that the organic-inorganic composite passivation coating treatment in steps S5 and S6 is omitted. That is, the primary hard carbon powder obtained in step S4 is not subjected to synergistic coating and subsequent heat treatment. The primary hard carbon powder is directly used as the final product. Other conditions are the same as in Example 4.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 4 is that the mixed acid solution in step S2 is replaced with an equal volume of dilute hydrochloric acid solution, that is, oxalic acid is not added during the acid washing and purification process, and other conditions are the same as in Example 4.

[0066] Comparative Example 4

[0067] The difference between this comparative example and Example 4 is that phytic acid is not added during the preparation of the modified impregnation solution, that is, the addition of 3 parts of phytic acid is omitted in step S3, and other conditions are the same as in Example 4.

[0068] Comparative Example 5

[0069] The difference between this comparative example and Example 4 is that tetraethyl orthosilicate is not added in step S5, that is, the addition of tetraethyl orthosilicate is omitted in the pre-hydrolysis process, so that the coating layer is composed only of nitrogen-doped carbon formed by the pyrolysis of polydopamine. Other conditions are the same as in Example 4.

[0070] Comparative Example 6

[0071] The difference between this comparative example and Example 4 is that pentaerythritol and citric acid are not added during the preparation of the modified impregnation solution. That is, in step S3, only phytic acid aqueous solution is used to treat the pure bamboo powder, and other conditions are the same as in Example 4.

[0072] Performance testing

[0073] The bamboo-based hard carbon anode materials prepared in Examples 1-4 and Comparative Examples 1-6 were used as active materials, and mixed with conductive agent SuperP and binder sodium carboxymethyl cellulose (CMC) at a mass ratio of 8:1:1. An appropriate amount of deionized water was added and stirred until homogeneous to prepare a uniform electrode slurry. The slurry was uniformly coated onto copper foil and dried in a vacuum drying oven at 60°C for 12 hours. The slurry was then cut into circular electrode sheets with a diameter of 12 mm. A sodium metal sheet was used as the counter electrode, and a Celgard membrane was used as the isolation layer. The electrolyte was a mixture of 1M NaPF6 dissolved in propylene carbonate (PC) and fluoroethylene carbonate (FEC) (volume ratio 9:1). CR2032 coin cells were assembled in an argon-atmospheric glove box. After standing for 24 hours, electrochemical performance was tested using a Blue Battery testing system in the voltage range of 0.01-2.5V. The initial discharge specific capacity and initial coulombic efficiency at a current density of 0.1A / g, and the capacity retention after 500 cycles at a current density of 1A / g were tested.

[0074] The performance of the bamboo-based hard carbon sodium-ion battery anode materials and their preparation methods in Examples 1-4 and Comparative Examples 1-6 were tested, and the test results are shown in Table 1.

[0075] Table 1

[0076] Example 1 334.5 87.6 91.4 Example 2 337.6 88.1 92.5 Example 3 341.7 89.4 93.7 Example 4 343.2 90.5 94.6 Comparative Example 1 264.8 70.5 62.4 Comparative Example 2 286.2 76.2 71.5 Comparative Example 3 306.5 83.6 85.3 Comparative Example 4 317.6 84.3 87.1 Comparative Example 5 326.8 85.4 89.5 Comparative Example 6 295.4 81.7 77.2

[0077] As shown in the table above, Example 4 achieved a reversible capacity of 343.2 mAh / g at a current density of 0.1 A / g, with an initial coulombic efficiency of 90.5% and a capacity retention rate of 94.6% after 500 cycles, demonstrating the most outstanding electrochemical sodium storage performance among all experimental groups.

[0078] Comparative Example 1, which omitted the multi-component in-situ impregnation modification treatment, saw a significant decrease in reversible capacity to 264.8 mAh / g and an initial coulombic efficiency as low as 70.5%. This indicates that the lack of the esterification cross-linking network formed by pentaerythritol and citric acid leads to microscopic collapse of the bamboo-based skeleton during the carbonization stage, resulting in a large number of open defects that irreversibly consume sodium ions. Comparative Example 2, which did not undergo subsequent organic and inorganic composite passivation coating treatment, saw its initial coulombic efficiency decrease to 76.2% and its cycle retention rate as low as 71.5%. This confirms that the artificial interface layer synergistically constructed by polydopamine and silica plays an irreplaceable core role in shielding active sites, inhibiting continuous electrolyte decomposition, and maintaining structural stability. Comparative Example 3, which replaced the mixed acid system with single dilute hydrochloric acid in the purification step, saw its reversible capacity decrease to 306.5 mAh / g and its initial efficiency decrease to 83.6%, demonstrating that the chemical chelating ability of oxalic acid is crucial for the complete removal of catalyst stones. The presence of impurity metals in the graphite and the protection of the disordered hard carbon structure, which is conducive to sodium storage, are of paramount importance. Comparative Example 4, which did not add phytic acid to the modified impregnation solution, showed a reversible capacity of 317.6 mAh / g, confirming that the in-situ phosphorus doping effect provided by phytic acid is the key chemical driving force for effectively expanding the interlayer spacing of graphite and improving the plateau capacity. Comparative Example 5, which omitted tetraethyl orthosilicate in the coating step, showed lower cycle stability and first-time efficiency than Example 4, indicating that the introduction of silica components can significantly improve the mechanical modulus and chemical resistance of the passivation layer, further optimizing the quality of the interfacial film through ion sieving effect. Comparative Example 6, which used only phytic acid without adding pentaerythritol and citric acid in the pretreatment, resulted in a reversible capacity of only 295.4 mAh / g, again demonstrating that only through deep chemical synergy between a multi-component crosslinking system and heteroatom doping can the technical challenge of balancing capacity and first-time efficiency in bamboo-based hard carbon be fundamentally solved.

[0079] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon sodium-ion battery anode material based on bamboo, characterized in that, Includes the following steps: S1. Remove the outer skin and nodes from the bamboo and cut it into blocks. After ultrasonic cleaning with deionized water, dry the bamboo and collect the bamboo powder by ball milling, crushing and sieving for later use. S2. Immerse the bamboo powder obtained in step S1 into a mixed acid solution, stir and react, then filter under reduced pressure, wash with water until neutral, and dry under vacuum to obtain pure bamboo powder. S3. Place pure bamboo powder in a vacuum mixer, start the mixer and add the modified impregnation liquid. Mix initially to form a slurry. Continue stirring under vacuum. After the vacuum is released, raise the temperature and continue stirring and reacting under normal pressure. Then, vacuum dry to obtain the modified bamboo powder precursor. S4. The modified bamboo powder precursor is placed in a tube furnace and high-purity argon is introduced. The temperature is programmed to complete the pre-carbonization. The temperature is then increased to carry out high-temperature carbonization. After completion, the mixture is naturally cooled to room temperature to obtain primary hard carbon powder. S5. Disperse primary hard carbon powder ultrasonically in a mixed solvent of anhydrous ethanol and deionized water to obtain dispersion A; dissolve dopamine hydrochloride in deionized water to obtain solution B; mix tris(hydroxymethyl)aminomethane buffer with tetraethyl orthosilicate and pre-hydrolyze to obtain solution C for later use. S6. Under the stirring of an ice-water bath, first add solution B dropwise to dispersion A, then add solution C dropwise to the mixed system. After the addition is complete, stir the reaction at room temperature in the dark. After centrifugation, washing, and vacuum drying, heat treatment is carried out in a tube furnace under high-purity argon gas. After ball milling, the product is sieved to obtain bamboo-based hard carbon sodium-ion battery anode material. The bamboo used in step S1 is 3-5 year old bamboo, and the size of the block is 1-2 cm. 3 The ultrasonic cleaning time is 30-40 minutes, the drying temperature is 60-70℃, and the particle size D of the resulting bamboo powder is... 50 The thickness is 20-40 μm; in step S2, the mixed acid solution is prepared from dilute hydrochloric acid and oxalic acid, the solid-liquid ratio of bamboo powder to the mixed acid solution is 1 g: (8-12) ml, the stirring reaction temperature is 80-90℃, the stirring speed is 300-350 rpm, and the reaction time is 2-3 h; in step S3, the pure bamboo powder is 20-25 parts, and the modified impregnation solution is 40-45 parts; the modified impregnation solution is prepared by dissolving pentaerythritol, citric acid, and phytic acid in deionized water; the modified impregnation solution is obtained by dissolving 3-5 parts pentaerythritol, 2-4 parts citric acid, and 1-3 parts phytic acid in 25-30 parts deionized water, and stirring at 70-80℃ and 400-450 rpm; in step S4, the pre-carbonization temperature is 300-400℃, the holding time is 2-2.5 h, and the heating rate is... The rate is 2-5℃ / min; the high-temperature carbonization temperature is 1200-1400℃, the holding time is 3-5h, and the heating rate is 3-5℃ / min; in step S5, the primary hard carbon powder is 10-15 parts, the mixed solvent is 70-80 parts, and the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is (1-3):1; dopamine hydrochloride is 0.8-1.5 parts, tris(hydroxymethyl)aminomethane buffer is 10-15 parts, and tetraethyl orthosilicate is 0.3-0.6 parts; in step S6, the stirring speed during the dropping process is 250-350rpm, the dropping rate of solution B is 1-3ml / min, and the stirring reaction time at room temperature in the dark is 12-16h; the heat treatment temperature is 600-650℃, the holding time is 1-2h, and the heating rate is 3-4℃ / min.

2. A bamboo-based hard carbon sodium-ion battery anode material, characterized in that, It is prepared by the method described in claim 1.

3. The bamboo-based hard carbon sodium-ion battery anode material according to claim 2, characterized in that, The material has a graphite interlayer spacing of 0.38-0.40 nm, a reversible capacity of ≥320 mAh / g at a current density of 0.1 A / g, and an initial coulombic efficiency of ≥87%.