Preparation method of stable hard carbon negative electrode material based on fast-growing eucalyptus

Abstract

The present application relates to the technical field of negative electrode material, and particularly relates to a preparation method of a stable hard carbon negative electrode material based on fast-growing eucalyptus, which is prepared by compounding and modifying fast-growing eucalyptus-based hard carbon powder with modified bentonite liquid, and the raw material composition comprises, by weight, 85-95 parts of fast-growing eucalyptus-based hard carbon powder and 5-15 parts of modified bentonite liquid. The present application utilizes the synergistic effect of the modified bentonite liquid and the fast-growing eucalyptus hard carbon, realizes the multiple modification effects of interface modification, ion conduction enhancement and structure support, and finally prepares the fast-growing eucalyptus-based hard carbon negative electrode material with excellent cycle stability, high initial coulomb efficiency and good rate performance, and solves the performance short board of the traditional fast-growing eucalyptus hard carbon.

Description

Technical Field

[0001] This invention relates to the field of anode material technology, specifically to a method for preparing stable hard carbon anode materials based on fast-growing eucalyptus. Background Technology

[0002] Under the "dual-carbon" strategy, my country is vigorously developing next-generation high-efficiency energy storage technologies. Sodium-ion batteries, due to their abundant raw material reserves, low cost, and high safety, have become a research hotspot in the field of electrochemical energy storage. High-performance anode materials are the core key to the industrialization of sodium-ion batteries. Hard carbon materials, with their layered disordered porous structure, good chemical stability, and sodium-ion intercalation-deintercalation performance, are among the most promising anode materials for sodium-ion batteries.

[0003] Biomass-based hard carbon uses agricultural and forestry waste as a precursor, possessing advantages such as being green and environmentally friendly, low-cost, and having a wide range of raw material sources, thus meeting the development requirements of waste recycling and carbon peaking and carbon neutrality. Fast-growing eucalyptus, a fast-growing and high-yield forest widely planted in southern my country, has a short growth cycle and high yield. Its wood structure has a suitable ratio of cellulose, hemicellulose, and lignin, which, after carbonization, can form hard carbon materials with good pore structure, making it a high-quality precursor for preparing biomass-based hard carbon anodes. However, traditional fast-growing eucalyptus-based hard carbon anode materials have the following technical problems: First, the microcrystalline structure of pure fast-growing eucalyptus hard carbon has high disorder, and structural collapse easily occurs during sodium ion intercalation-deintercalation, leading to insufficient cycle stability; second, the surface of hard carbon has many defect sites, which easily form an irreversible solid electrolyte interphase (SEI) film during the first charge-discharge process, resulting in low initial coulombic efficiency; third, the ion conduction rate of hard carbon is slow, resulting in poor rate performance at high current densities, limiting its application in high-power energy storage batteries.

[0004] Currently, existing technologies for modifying biomass hard carbon anodes mainly employ methods such as atomic doping, carbon coating, and composite inorganic nanoparticles. However, these methods still have shortcomings: for example, atomic doping is complex and the doping amount is difficult to control; carbon coating easily leads to blockage of hard carbon channels, affecting ion transport; and the interfacial bonding of single inorganic nanoparticle composites is weak, making them prone to detachment during cycling, resulting in poor long-term modification effects. Bentonite, as a layered silicate mineral, has good ion exchange capacity, dispersibility, and structural support. After modification, it can be combined with biomass hard carbon to provide channels for sodium ion transport using its layered structure, while also leveraging its structural support to inhibit hard carbon collapse. However, current technologies have not applied modified bentonite solutions to the modification of fast-growing eucalyptus hard carbon, and lack targeted modification of bentonite and synergistic design of functional components, thus failing to fully realize its modification effects. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the purpose of this invention is to provide a lightweight, high-toughness concrete and its preparation method to solve the problems mentioned in the background art.

[0006] The present invention solves the technical problem by adopting the following technical solution: This invention provides a stable hard carbon anode material based on fast-growing eucalyptus, which is prepared by composite modification of fast-growing eucalyptus-based hard carbon powder and modified bentonite liquid. By weight, the raw material composition is: 85-95 parts of fast-growing eucalyptus-based hard carbon powder and 5-15 parts of modified bentonite liquid.

[0007] Core Modifying Component: Preparation of Modified Bentonite Solution The core innovation of this invention lies in the design and preparation of modified bentonite liquid. Through high-temperature pretreatment of bentonite, functional component compounding, and ball milling compounding with the modified body, the bentonite liquid is endowed with multiple functions such as interface modification, enhanced ion conduction, structural support, and defect passivation. The preparation method includes four steps, as follows: The bentonite pretreatment involves placing sodium-based bentonite in a heat treatment furnace and heat-treating it at 155-165℃ for 15-20 minutes to remove adsorbed water and water of crystallization. Then, it is heated to 270-280℃ at a slow heating rate of 2-5℃ / min and held for 1 hour to moderately exfoliate the layered structure of the bentonite, increasing its specific surface area and ion exchange sites. Finally, it is air-cooled to room temperature with the furnace to obtain pretreated bentonite. Mechanism of action: High-temperature pretreatment removes moisture from the bentonite, preventing the formation of bubbles during subsequent carbonization; slow heating achieves gentle exfoliation of the layered structure, ensuring ion transport channels without damaging the integrity of the layered structure, thus providing a foundation for subsequent loading of functional components.

[0008] Bentonite solution preparation: By weight, 5-8 parts of pretreated bentonite, 2-5 parts of nano-lanthanum oxide, 4-7 parts of sodium alginate solution (8-10% by mass), and 1-3 parts of nano-silicon carbide are mixed and stirred at 300-500 r / min for 40-60 min until homogeneous, thus obtaining the bentonite solution. Mechanism of action: Nano-lanthanum oxide, a rare earth metal oxide, can passivate defect sites on the surface of hard carbon, reduce the formation of irreversible SEI films, and improve the first coulombic efficiency; nano-silicon carbide has high hardness and high chemical stability, and can act as a structural support, inhibiting the volume expansion and structural collapse of hard carbon during cycling; sodium alginate, as a natural polymeric dispersant, can improve the dispersibility of bentonite, lanthanum oxide, and silicon carbide, while its hydroxyl and carboxyl groups can form hydrogen bonds with the surface of hard carbon, enhancing the interfacial bonding force between the modified bentonite solution and hard carbon.

[0009] Preparation of the modified body: By weight, 3-5 parts hexagonal boron nitride, 2-4 parts carbon nanotubes, and 1-3 parts nano-yttrium oxide were placed in a sintering furnace and sintered at 300-350℃ for 1 hour, then naturally cooled to room temperature to obtain the modified body. Mechanism of action: Hexagonal boron nitride has a graphite-like layered structure and excellent thermal and electrical conductivity, providing a fast channel for sodium ion transport and improving the thermal stability of the material; carbon nanotubes have a high aspect ratio and excellent electrical conductivity, forming a conductive network in hard carbon and improving the electron conduction rate; nano-yttrium oxide can weakly interact with sodium ions, regulating the intercalation-extraction behavior of sodium ions, and further passivating defect sites. The modified body formed by the sintering and combination of the two can synergistically improve the ion / electron conduction rate and cycle stability of hard carbon.

[0010] The modified bentonite slurry was mixed with the modified material and bentonite slurry at a weight ratio of (5~7):3 and placed in a ball mill. The mixture was milled at 1000~1500 r / min for 2 hours using zirconia balls as the milling medium, with a material-to-ball ratio of 1:6, to obtain the modified bentonite slurry. Mechanism of action: High-speed ball milling causes physical intercalation and microscale composite formation of the components of the modified material and bentonite slurry, forming a uniform functional composite system. The mechanical force generated during ball milling further refines the layered structure of the bentonite, increasing sodium ion transport sites. Simultaneously, it ensures that the conductive components of the modified material are uniformly loaded between the bentonite layers, achieving a synergistic effect of "ion conduction + electronic conduction + structural support".

[0011] The overall synergistic mechanism of modified bentonite liquid: The layered structure of modified bentonite liquid provides a rapid transport channel for sodium ion intercalation / deintercalation, improving rate performance; Lanthanum oxide and yttrium oxide passivate the defect sites on the surface of hard carbon, reducing the formation of irreversible SEI film and improving the first coulombic efficiency; Silicon carbide and hexagonal boron nitride form a three-dimensional structural support network, inhibiting the volume expansion and structural collapse of hard carbon during cycling, and improving cycling stability; Carbon nanotubes construct a conductive network, improving the electronic conduction rate of the material; Sodium alginate enhances the interfacial bonding force between modified bentonite liquid and hard carbon, preventing the modified components from falling off during cycling and ensuring the long-term effectiveness of the modification.

[0012] Preparation of fast-growing eucalyptus-based hard carbon powder Fast-growing eucalyptus-based hard carbon powder is prepared using a directional carbonization process. This process involves removing volatile components through low-temperature carbonization and regulating the microcrystalline and pore structures through high-temperature carbonization. Specifically, the fast-growing eucalyptus raw material is dried, pulverized, and granulated. Then, under nitrogen protection, it undergoes sequential low-temperature carbonization at 300-350℃ and high-temperature carbonization at 1000-1200℃. After acid washing with dilute hydrochloric acid to remove impurities, drying, pulverizing, and sieving, fast-growing eucalyptus-based hard carbon powder with a particle size D50 of 10-15μm, a specific surface area of ​​4-6m² / g, and an average pore size of 9-11nm is obtained. Key process points: Low-temperature carbonization removes volatile components such as hemicellulose from fast-growing eucalyptus, preventing excessive pore development during high-temperature carbonization; high-temperature carbonization regulates the microcrystalline disorder and pore structure of the hard carbon, forming a porous structure suitable for sodium ion intercalation and deintercalation; simultaneously, acid washing removes ash impurities from the raw material, improving the purity and electrochemical performance of the hard carbon.

[0013] Preparation method of stable hard carbon anode material based on fast-growing eucalyptus The anode material preparation method of this invention follows the process route of "raw material pretreatment - directional carbonization - acid washing and impurity removal - modification and compounding - high-temperature calcination". By optimizing the parameters of each step, it ensures that the modified bentonite liquid and fast-growing eucalyptus hard carbon powder are uniformly compounded to give full play to the modification effect. The specific steps are as follows: S1: Pretreatment of fast-growing eucalyptus raw materials. Remove impurities such as bark and branches from fast-growing eucalyptus wood, cut it into small pieces of 1-2cm, and dry it in a drying oven at 80-100℃ for 12-24h until the moisture content is ≤5%. After being crushed by a pulverizer, it is passed through a 40-60 mesh sieve and then granulated by a granulator to obtain particles with a particle size of 2-5mm, thus obtaining fast-growing eucalyptus pretreated particles. Key points of the process: control the moisture content of the raw materials to ≤5% to avoid the generation of air bubbles during carbonization, which would lead to uneven pore structure; granulation forms uniform particles to ensure uniform heating during the carbonization process.

[0014] S2: Low-temperature carbonization involves placing pre-treated fast-growing eucalyptus granules into a continuous carbonization furnace and heating them to 300-350℃ at a heating rate of 5-8℃ / min under nitrogen protection (gas flow rate 20-30 mL / min), holding at this temperature for 2-3 hours to obtain low-temperature carbonized material. Key process points: Nitrogen protection prevents raw material oxidation; low-temperature carbonization removes volatile components and initially forms a carbon skeleton, laying the foundation for high-temperature carbonization.

[0015] S3: High-temperature carbonization involves heating the low-temperature carbonized material to 1000-1200℃ under nitrogen protection (gas flow rate 20-30 mL / min) at a heating rate of 3-5℃ / min, holding at this temperature for 3-4 hours, and then naturally cooling to room temperature to obtain fast-growing eucalyptus-based carbonized material. Key process points: Slow heating rate to avoid cracking of the carbon skeleton; high-temperature carbonization at 1000-1200℃ forms hard carbon with a disordered layered structure, whose pore structure is suitable for the intercalation and deintercalation of sodium ions.

[0016] S4: Acid Washing and Impurity Removal. Add fast-growing eucalyptus-based carbonized material to 5-8% (w / w) dilute hydrochloric acid at a solid-liquid ratio of 1:10. Stir at 60-70℃ for 2-3 hours. After filtration, wash with deionized water until the pH of the filtrate reaches 6.5-7.5. Dry in a 105-110℃ drying oven for 6-8 hours to obtain the acid-washed carbonized material. Key Process Points: Dilute hydrochloric acid removes ash impurities such as potassium, calcium, and magnesium from the carbonized material, reducing the impact of impurities on electrochemical performance; washing with water to neutrality avoids acid residue leading to internal battery corrosion.

[0017] S5: Crushing and Screening. The acid-washed charcoal is crushed using an ultra-fine pulverizer and passed through a 100-200 mesh sieve to obtain fast-growing eucalyptus-based hard charcoal powder with a particle size D50 of 10-15 μm. Key process points: Controlling the powder particle size to 10-15 μm ensures both the tap density of the material and avoids excessively small particle size leading to an excessively large specific surface area and reduced initial coulombic efficiency.

[0018] S6: Modified Bentonite Liquid Composite: By weight, 85-95 parts of fast-growing eucalyptus-based hard carbon powder are mixed with 5-15 parts of modified bentonite liquid. Anhydrous ethanol is added as the dispersion medium, with a solid-liquid ratio of 1:5. The mixture is ultrasonically dispersed for 30-40 minutes (ultrasonic power 300-400W), and then stirred and evaporated at 80-90℃ until no ethanol residue remains, yielding the composite precursor. Key Process Points: Anhydrous ethanol is used as the dispersion medium to improve the dispersion uniformity of the hard carbon powder and the modified bentonite liquid; ultrasonic dispersion avoids the agglomeration of the modified components, ensuring that the modified bentonite liquid uniformly coats the surface of the hard carbon powder and fills the pores.

[0019] S7: High-temperature calcination involves heating the composite precursor to 800-900℃ under argon protection (gas flow rate 20-30 mL / min) at a heating rate of 4-6℃ / min, holding for 2 hours, and then naturally cooling to room temperature to obtain a stable hard carbon anode material based on fast-growing eucalyptus. Key process points: Argon protection prevents material oxidation; high-temperature calcination at 800-900℃ enhances the interfacial bonding between the modified bentonite solution and the hard carbon, while also making the SEI film more stable and improving the electrochemical performance of the material.

[0020] S8: Post-processing involves removing magnetic impurities from the calcined material using a demagnetizer, then sieving it through a 200-mesh sieve to remove excessively large particles, resulting in the finished negative electrode material.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This invention uses fast-growing eucalyptus as a biomass precursor and controls the pore structure and microcrystalline morphology of hard carbon through a directional carbonization process to reduce defect sites. At the same time, a special modified bentonite liquid is designed. Bentonite is pretreated at high temperature and then compounded with functional components such as lanthanum oxide and silicon carbide. Then, it is ball-milled and compounded with an improved body prepared by boron nitride and carbon nanotubes. By utilizing the synergistic effect of the modified bentonite liquid and fast-growing eucalyptus hard carbon, multiple modification effects such as interface modification, enhanced ion conduction, and structural support are achieved. Finally, a fast-growing eucalyptus-based hard carbon anode material with excellent cycle stability, high initial coulombic efficiency, and good rate performance is prepared, which solves the performance shortcomings of traditional fast-growing eucalyptus hard carbon. A specially designed modified bentonite solution was designed to achieve multiple synergistic modifications: Overcoming the shortcomings of existing single modification methods, bentonite was pretreated at high temperature and then combined with lanthanum oxide and silicon carbide. This mixture was then ball-milled with an improved body prepared from boron nitride / carbon nanotubes / yttrium oxide, forming a multifunctional modified bentonite solution that combines interface modification, enhanced ion conduction, improved electronic conduction, structural support, and defect passivation. This achieves multiple synergistic modifications of fast-growing eucalyptus hard charcoal while simultaneously solving the problems of weak interfacial bonding and easy detachment of the modified components. Directional carbonization process for fast-growing eucalyptus char: Targeting the wood composition characteristics of fast-growing eucalyptus, a directional carbonization process of "low-temperature carbonization + high-temperature carbonization" is designed. Low-temperature carbonization removes volatile components, while high-temperature carbonization regulates the disordered layered structure and porous structure of the char, forming a pore structure suitable for sodium ion intercalation and deintercalation (specific surface area 4~6 m² / g, average pore size 9~11 nm). At the same time, it reduces surface defect sites and improves the basic electrochemical performance of the char. The uniform composite process of modified bentonite liquid and fast-growing eucalyptus char: The composite process of "ultrasonic dispersion + high temperature calcination" is adopted. The dispersion effect of anhydrous ethanol and the deagglomeration effect of ultrasound are used to ensure that the modified bentonite liquid is uniformly coated on the surface of the char powder and fills the pores. Then, high temperature calcination is carried out to enhance the interfacial bonding force, so that the modified components and char form a whole and ensure the long-term effect of modification. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. The embodiments given are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. All electrochemical performance tests were performed in accordance with the "Technical Requirements for Hard Carbon Anode Materials for Sodium-ion Batteries" T / DCB 010-2024. The test conditions were: battery test voltage range 0.01~1.5V, electrode sheet density 5~9mg / cm², and test temperature 25±2℃. Cycle performance tests were conducted at a current density of 50mA / g, and rate performance tests were conducted at current densities of 50mA / g, 100mA / g, 200mA / g, and 500mA / g.

[0024] Example 1 (Optimal Solution of the Invention) Raw material ratio: by weight, 90 parts of fast-growing eucalyptus-based hard carbon powder and 10 parts of modified bentonite liquid.

[0025] Preparation of modified bentonite liquid (1) Bentonite pretreatment: Sodium-based bentonite was heat-treated at 160℃ for 18 min, heated to 275℃ at 3℃ / min, kept at 1 h, and air-cooled to room temperature; (2) Bentonite liquid: 6 parts of pretreated bentonite, 3 parts of nano lanthanum oxide (20nm), 5 parts of 9% sodium alginate solution, 2 parts of nano silicon carbide (40nm), stirred at 400r / min for 50 min; (3) Improved body: 4 parts of hexagonal boron nitride, 3 parts of carbon nanotubes (15nm / 3μm), 2 parts of nano yttrium oxide (30nm), sintered at 320℃ for 1 h; (4) Composite ball milling: The improved body and bentonite liquid were mixed at 6:3, ball milled at 1200r / min for 2 h, with a material-to-ball ratio of 1:6, to obtain modified bentonite liquid.

[0026] Preparation of fast-growing eucalyptus-based hard carbon powder: After drying, crushing and granulating, fast-growing eucalyptus raw materials were carbonized at a low temperature of 320℃ for 2.5h, carbonized at a high temperature of 1100℃ for 3.5h, and acid-washed with 6% dilute hydrochloric acid for 2.5h. After crushing and sieving, hard carbon powder with D50=13μm, specific surface area of ​​5.2m² / g and average pore size of 10.1nm was obtained.

[0027] Preparation of negative electrode material S1~S5: Prepare fast-growing eucalyptus-based hard carbon powder according to the above process; S6: Add 90 parts of hard carbon powder + 10 parts of modified bentonite liquid, add anhydrous ethanol, sonicate at 350W for 35min, stir and evaporate at 85℃ until no ethanol residue remains; S7: Under argon protection, heat to 850℃ at 5℃ / min, hold for 2h, and air cool; S8: Demagnetize and sieve to obtain the finished negative electrode material.

[0028] Example 2

[0029] The difference from Example 1 is that: 95 parts of fast-growing eucalyptus-based hard carbon powder and 5 parts of modified bentonite liquid were used; the modified material and bentonite liquid were mixed at a ratio of 5:3. The remaining raw material ratios and preparation processes were the same as in Example 1.

[0030] Example 3

[0031] The difference from Example 1 is that: 85 parts of fast-growing eucalyptus-based hard carbon powder and 15 parts of modified bentonite liquid were used; the modified material and bentonite liquid were mixed at a ratio of 7:3. The remaining raw material ratios and preparation processes were the same as in Example 1.

[0032] Comparative Example 1 The difference from Example 1 is that no modified bentonite liquid was added; instead, fast-growing eucalyptus-based hard carbon powder was directly calcined at 850°C and used as the negative electrode material. All other preparation processes were the same as in Example 1.

[0033] Comparative Example 2 The difference from Example 1 is that no modifier was added in the preparation of the modified bentonite liquid; the bentonite liquid was used directly as the modifier. All other raw material ratios and preparation processes are the same as in Example 1.

[0034] Comparative Example 3 The difference from Example 1 is that no nano-silicon carbide and nano-lanthanum oxide were added in the preparation of the bentonite slurry. It was prepared by mixing pretreated bentonite and sodium alginate solution, and then ball-milling it with the modified body to obtain the modified bentonite slurry. The remaining raw material ratios and preparation processes are the same as in Example 1.

[0035] Performance test results The performance test results of each embodiment and comparative example are shown in Table 1:

[0036] Test Result Analysis As shown in Table 1, the stable hard carbon anode materials based on fast-growing eucalyptus prepared in Examples 1-3 of this invention possess excellent electrochemical performance, showing significant advantages compared to the comparative examples. Specific analysis is as follows: Examples 1-3 exhibit excellent performance, with Example 1 being the optimal solution: The anode materials of Examples 1-3 have a charging specific capacity ≥310mAh / g at a current density of 50mA / g, an initial coulombic efficiency ≥92.0%, a capacity retention rate ≥91.0% after 1000 cycles, and a capacity retention rate ≥85.0% at a high current density of 500mA / g. The specific surface area and tap density both meet the technical requirements for hard carbon anodes in sodium-ion batteries. Among them, Example 1 (with 10 parts of modified bentonite liquid added and a ratio of 6:3 between the modified material and the bentonite liquid) has the best performance in all aspects and is the optimal solution of this invention.

[0037] Comparative Example 1 (without modified bentonite solution) showed significant performance degradation, verifying the core role of modified bentonite solution: the pure fast-growing eucalyptus hard carbon anode without modified bentonite solution had a charging specific capacity of only 285.4 mAh / g, an initial coulombic efficiency of 88.6%, and a capacity retention rate of only 75.2% after 1000 cycles, exhibiting extremely poor rate performance. This indicates that pure fast-growing eucalyptus hard carbon has inherent problems such as insufficient structural stability, numerous defect sites, and slow ion conduction rate. Modified bentonite solution is the core component for improving its electrochemical performance and is indispensable.

[0038] Comparative Example 2 (without the modified component) showed a performance decline, verifying the key role of the modified component: Without the addition of the modified component, the various properties of the negative electrode material in the modified bentonite solution were significantly reduced compared to Example 1. The charge specific capacity decreased by 21.4 mAh / g, the cycle retention rate decreased by 8.9%, and the rate performance also decreased significantly. This is because boron nitride and carbon nanotubes in the modified component are key to improving the ion / electron conduction rate, and yttrium oxide can further passivate defect sites. After its absence, the ion / electron conduction enhancement effect of the modified bentonite solution was greatly weakened, and the modification effect could not be fully utilized, proving that the modified component is an important component of the modified bentonite solution.

[0039] Comparative Example 3 (bentonite solution without silicon carbide and lanthanum oxide) showed poor performance, verifying the synergistic effect of functional components: Without the addition of silicon carbide and lanthanum oxide to the bentonite solution, the initial coulombic efficiency and cycle stability of the anode material decreased significantly, indicating that the defect passivation effect of lanthanum oxide and the structural support effect of silicon carbide are the key to improving the initial coulombic efficiency and cycle stability. The two form a synergistic effect with the layered structure of bentonite. The defect passivation and structural support effects of the modified bentonite solution are greatly reduced after their absence, further proving the synergistic necessity of each functional component in the modified bentonite solution.

[0040] Effect of modified bentonite liquid addition amount: The performance of Example 2 (5 parts) and Example 3 (15 parts) was slightly lower than that of Example 1 (10 parts), indicating that there is an optimal addition amount of modified bentonite liquid. If the addition amount is too small, the modification effect will be insufficient, and if the addition amount is too large, it will block some of the pores of hard carbon, affect the intercalation and deintercalation of sodium ions, and lead to a slight decrease in specific capacity and rate performance.

[0041] Advantages compared to existing technologies The stable hard carbon anode material based on fast-growing eucalyptus prepared by this invention and its preparation method have the following significant advantages compared with the prior art: Excellent electrochemical performance, with superior stability and rate performance: The synergistic effect of modified bentonite liquid and fast-growing eucalyptus hard carbon enables the anode material to achieve a charge specific capacity of 310~325mAh / g, an initial coulombic efficiency ≥92.0%, a capacity retention rate of ≥91.0% after 1000 cycles, and a capacity retention rate of ≥85.0% at a rate of 500mA / g. This solves the technical problems of insufficient cycle stability, low initial coulombic efficiency, and poor rate performance of traditional fast-growing eucalyptus hard carbon, and all performance characteristics meet the high-end requirements of hard carbon anodes for sodium-ion batteries.

[0042] Multiple synergistic modifications ensure long-lasting and stable modification effects: The modified bentonite liquid integrates interface modification, ion conduction enhancement, electronic conduction improvement, structural support, and defect passivation to achieve multiple synergistic modifications; at the same time, through ultrasonic dispersion and high-temperature calcination processes, the modified bentonite liquid and hard carbon form a strong interfacial bond, preventing the modified components from falling off during the cycle and ensuring the long-lasting effect of the modification.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0044] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A stable hard carbon anode material based on fast-growing eucalyptus, characterized in that, It is prepared by compound modification of fast-growing eucalyptus-based hard carbon powder and modified bentonite liquid. By weight, the raw material composition is: 85-95 parts of fast-growing eucalyptus-based hard carbon powder and 5-15 parts of modified bentonite liquid. The modified bentonite liquid is prepared by pre-treating bentonite, compounding it with functional components, and then ball milling it with the modified body. It is used to improve the cycle stability, ion conductivity and structural integrity of hard carbon anode.

2. The stable hard carbon anode material based on fast-growing eucalyptus according to claim 1, characterized in that, The preparation method of the modified bentonite liquid includes four steps: bentonite pretreatment, bentonite liquid preparation, modified body preparation, and composite ball milling.

3. The stable hard carbon anode material based on fast-growing eucalyptus according to claim 2, characterized in that, The specific preparation method of modified bentonite solution is as follows: (1) Bentonite pretreatment: Sodium-based bentonite is placed in a heat treatment furnace and heat-treated at 155~165℃ for 15~20min. Then, it is heated to 270~280℃ at a heating rate of 2~5℃ / min and held for 1h. It is then air-cooled to room temperature with the furnace to obtain pretreated bentonite. (2) Preparation of bentonite solution: By weight, 5-8 parts of pretreated bentonite, 2-5 parts of nano lanthanum oxide, 4-7 parts of sodium alginate solution with a mass fraction of 8-10% and 1-3 parts of nano silicon carbide are mixed and stirred at 300-500 r / min for 40-60 min until uniformly mixed to obtain bentonite solution; (3) Improved preparation of the body; (4) Composite ball milling: Mix the modified body and bentonite liquid at a weight ratio of (5~7):3, put them into a ball mill, and ball mill at a speed of 1000~1500r / min for 2h. The ball milling medium is zirconia balls, and the material-to-ball ratio is 1:6 to obtain modified bentonite liquid.

4. The stable hard carbon anode material based on fast-growing eucalyptus according to claim 3, characterized in that, The method for preparing the improved body is as follows: By weight, 3-5 parts of hexagonal boron nitride, 2-4 parts of carbon nanotubes and 1-3 parts of nano-yttrium oxide were placed in a sintering furnace and sintered at 300-350°C for 1 hour, and then naturally cooled to room temperature to obtain the improved body.

5. The stable hard carbon anode material based on fast-growing eucalyptus according to claim 3, characterized in that, The nano-lanthanum oxide particles have a diameter of 10-30 nm, the nano-silicon carbide particles have a diameter of 30-60 nm, the carbon nanotubes have a diameter of 10-20 nm and a length of 1-5 μm, and the nano-yttrium oxide particles have a diameter of 20-40 nm.

6. The stable hard carbon anode material based on fast-growing eucalyptus according to claim 1, characterized in that, The preparation process of the fast-growing eucalyptus-based hard carbon powder is as follows: After drying, crushing, and granulation, fast-growing eucalyptus raw materials are subjected to low-temperature carbonization, high-temperature carbonization, acid washing to remove impurities, drying, crushing, and sieving in sequence to obtain fast-growing eucalyptus-based hard carbon powder with a particle size D50 of 10~15μm, a specific surface area of ​​4~6m² / g, and an average pore size of 9~11nm.

7. A method for preparing a stable hard carbon anode material based on fast-growing eucalyptus as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Pretreatment of fast-growing eucalyptus raw materials: Remove impurities from fast-growing eucalyptus wood, cut it into small pieces, dry it in an 80~100℃ drying oven for 12~24h until the moisture content is ≤5%, crush it by a pulverizer and pass it through a 40~60 mesh sieve, and then granulate it into particles with a particle size of 2~5mm to obtain fast-growing eucalyptus pretreated particles. S2: Low-temperature carbonization: Fast-growing eucalyptus pretreated particles are placed in a continuous carbonization furnace and heated to 300-350°C at a heating rate of 5-8°C / min under nitrogen protection, and held for 2-3 hours to obtain low-temperature carbonized material; S3: High-temperature carbonization: The low-temperature carbonized material is heated to 1000~1200℃ under nitrogen protection at a heating rate of 3~5℃ / min, held at that temperature for 3~4h, and then naturally cooled to room temperature to obtain fast-growing eucalyptus-based carbonized material; S4: Acid washing to remove impurities: Add fast-growing eucalyptus carbonized material to dilute hydrochloric acid with a mass fraction of 5-8%, solid-liquid ratio of 1:10, stir at 60-70℃ for 2-3 hours, filter, wash with deionized water until neutral, and dry in a drying oven at 105-110℃ for 6-8 hours to obtain acid-washed carbonized material. S5: Crushing and sieving: The acid-washed charcoal is crushed by an ultra-micro pulverizer and passed through a 100-200 mesh sieve to obtain fast-growing eucalyptus-based hard charcoal powder with a particle size D50 of 10-15 μm; S6: Modified bentonite liquid composite: By weight, 85-95 parts of fast-growing eucalyptus-based hard carbon powder are mixed with 5-15 parts of modified bentonite liquid, anhydrous ethanol is added as the dispersion medium, the solid-liquid ratio is 1:5, ultrasonically dispersed for 30-40 min, and then stirred and evaporated at 80-90℃ until no ethanol residue remains, to obtain the composite precursor. S7: High-temperature calcination: The composite precursor is calcined under argon protection and then naturally cooled to room temperature to obtain a stable hard carbon anode material based on fast-growing eucalyptus. S8: Post-processing: The calcined material is demagnetized and sieved to remove impurity particles, resulting in the finished negative electrode material.

8. The preparation method according to claim 7, characterized in that, In steps S2, S3, and S7, an inert gas protective atmosphere is used, with a gas flow rate of 20-30 mL / min; in step S4, the dilute hydrochloric acid is analytical grade hydrochloric acid, which is washed with water after acid washing until the pH of the filtrate is 6.5-7.

5.

9. The preparation method according to claim 7, characterized in that, The ultrasonic power of ultrasonic dispersion in S6 is 300~400W.

10. The preparation method according to claim 7, characterized in that, The calcination process involves heating to 800-900℃ at a heating rate of 4-6℃ / min and holding at that temperature for 2 hours.

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