Preparation method of bamboo-based hard carbon sodium ion battery negative electrode material

Abstract

The invention belongs to the technical field of new energy materials, and particularly relates to a preparation method of a bamboo-based hard carbon sodium ion battery negative electrode material, which specifically comprises the following steps: (1) slicing, crushing, screening, sieving, drying and treating fresh bamboo under steam pressure to obtain bamboo powder; (2) bamboo powder and lactococcus lactis liquid are mixed and fermented, and after fermentation is completed, the bamboo powder and the lactococcus lactis liquid are washed to be neutral and dried; (3) placing the bamboo powder subjected to fermentation treatment in an inert atmosphere, heating, keeping constant temperature, and cooling to obtain a pre-carbonized sample; (4) soaking the pre-carbonized sample in a hydrochloric acid solution, continuously reacting, washing to be neutral, and drying; and (5) continuously heating the acid-washed and dried material in the step (4) in the inert atmosphere, carbonizing at a constant temperature, and cooling to obtain the final sodium-ion battery negative electrode material. The method disclosed by the invention has the advantages of remarkable environmental friendliness, low cost, simplicity and convenience in operation and the like; and the battery negative electrode material prepared by the method disclosed by the invention has excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials, and particularly relates to a preparation method of a bamboo-based hard carbon sodium ion battery negative electrode material. BACKGROUND

[0002] Lithium resources are increasingly exhausted and prices continue to rise. Finding a lower-cost and more abundant alternative system has become a research hotspot in the energy storage field. Sodium ion batteries are considered a powerful supplement to lithium ion batteries due to their abundant sodium resources, wide distribution, and low cost, and are particularly suitable for large-scale energy storage systems with medium and low energy density requirements. However, due to the larger radius of sodium ions (1.02 Å) than that of lithium ions (0.76 Å), the insertion efficiency of sodium ions in traditional graphite negative electrodes is extremely low, resulting in extremely limited capacity, which seriously hinders the development of sodium ion batteries. Therefore, developing alternative negative electrode materials suitable for sodium ion energy storage has become a key issue. Hard carbon is considered one of the most promising negative electrode materials for sodium ion batteries due to its high theoretical specific capacity (300-400 mAh / g), good cycle stability, suitable potential platform (0.1-0.8 V vs Na + / Na), and good compatibility with sodium ions. The sodium storage mechanism of hard carbon includes multiple paths such as surface adsorption, pore filling, and intercalation between graphite layers. The pore structure characteristics of the material (including pore size distribution, pore connectivity, and specific surface area) directly determine the sodium storage capacity and rate performance of the material.

[0003] Bamboo is a renewable natural resource with the advantages of short growth cycle, high carbon content (about 45-50%), uniform structure, and high mechanical strength, with an annual global production of over 300 million tons, making it an ideal carbon source for preparing hard carbon materials. However, the complex biological structure of bamboo poses significant challenges to the preparation of hard carbon materials. Bamboo powder is mainly composed of cellulose (35-45%), hemicellulose (20-30%), and lignin (20-25%), which are tightly cross-linked through hydrogen bonds, covalent bonds, and van der Waals forces to form a stable and dense three-dimensional network structure. Among them, cellulose is composed of glucose units connected by β-1,4 glycosidic bonds, showing a structure with coexisting crystalline and amorphous regions; hemicellulose is a branched amorphous polysaccharide composed of xylose, mannose, and arabinose; lignin is an aromatic polymer formed by the three-dimensional cross-linking of different aromatic monomers (such as coniferyl alcohol, cinnamyl alcohol, and sinapyl alcohol) through ester and ether bonds. This structure is difficult to be fully decomposed during high-temperature carbonization, leading to the following problems: ① volatile gases (such as CO, CO2, H2O, CH4) are difficult to release in the dense structure, easily forming closed pores or disordered large pore structures with low porosity and uneven distribution; ② the carbon skeleton shrinks and stacks during pyrolysis, lacking a conductive network, which limits the transmission paths of electrons and ions; ③ the ion channels between the layers are limited, and the electrolyte has poor wettability, which seriously restricts the rate performance and cycle stability of the material.

[0004] To overcome the above structural defects and improve the sodium storage performance of bamboo-based hard carbon materials, researchers have proposed various pretreatment methods to improve the microstructure of bamboo. Traditional physical methods such as mechanical crushing, ball milling and ultrasonic treatment can destroy the macrostructure of bamboo to some extent, but it is difficult to effectively control the ordered network at the molecular scale, and the energy consumption is high; chemical pretreatment methods usually use strong acids (such as H2SO4, HCl), strong bases (such as NaOH, KOH) or organic solvents to partially deconstruct the raw materials, which is effective for removing hemicellulose and lignin, but often accompanied by the following problems: ① harsh operating conditions (high temperature and pressure or strong corrosive environment) and high equipment requirements; ② large amount of chemical reagent consumption and high processing cost; ③ large amount of waste liquid generated and high pollution risk; ④ easy to destroy the cellulose skeleton, affecting the strength of the final carbon skeleton and conductivity; ⑤ difficult to achieve "selective" deconstruction of different components, and lack of control precision. In addition, the green technologies such as hydrothermal treatment and microwave-assisted treatment that have emerged in recent years have improved in efficiency and environmental friendliness, but still face problems such as expensive processing equipment, complex operation process and high energy consumption. Therefore, developing a green, selective, low-cost and excellent structure control method has become a key technical bottleneck for the preparation of high-performance bamboo-based hard carbon materials. Based on this idea, the present invention proposes to use lactic acid bacteria fermentation to enzymatically decompose and structure the bamboo, which greatly improves the efficiency of pore structure control and electrochemical performance while ensuring the integrity of the carbon skeleton, providing an effective path for the development of a new generation of high-performance sodium ion battery anode materials. SUMMARY

[0005] The present invention aims to solve the above technical problems and provides a method for preparing a bamboo-based hard carbon sodium ion battery anode material, which has the advantages of environmental friendliness, low cost and simple operation, and can avoid the high pollution and high energy consumption problems of traditional chemical treatment methods. The battery anode material prepared by the method has excellent electrochemical performance.

[0006] The technical solution of the present invention is as follows: A method for preparing a bamboo-based hard carbon sodium ion battery anode material, comprising the following steps: (1) Bamboo powder pretreatment: fresh bamboo is sliced, crushed, sieved and dried to obtain dried bamboo powder, which is treated under a steam pressure of 0.1-0.3 MPa for 20-40 min to obtain bamboo powder; (2) Lactic acid bacteria fermentation pretreatment: mix the bamboo powder with lactococcus lactis solution and ferment in an anaerobic environment in a constant temperature incubator, control the fermentation temperature at 30-60℃, and the fermentation time is 6-24h, after fermentation, wash with deionized water until neutral, and dry; (3) Pre-carbonization treatment: The bamboo powder after fermentation treatment in step (2) is placed in an inert atmosphere, heated to 400-600℃, and kept constant temperature for 6-12h, and the pre-carbonized sample is obtained after cooling; (4) Pickling and impurity removal treatment: The pre-carbonized sample obtained in step (3) is soaked in a 0.5-2mol / L hydrochloric acid solution, reacted at 50-90℃ for 3-6h, then washed with deionized water until neutral, and dried at 60-120℃ for 6-12h; (5) High-temperature carbonization forming: The material after acid washing and drying in step (4) is continuously heated to 1200-1400℃ in an inert atmosphere, and carbonized at constant temperature for 1-3h, and the final sodium ion battery negative electrode material is obtained after cooling.

[0007] The present application adopts lactic acid bacteria fermentation to pretreat bamboo powder, and uses the natural advantages of microbial metabolism to realize precise modification of bamboo structure. In the anaerobic fermentation process, the cellulase and hemicellulase (including beta-glucosidase, xylanase, etc.) secreted by lactic acid bacteria can specifically break the beta-1,4 glycosidic bond of cellulose and the branched structure of hemicellulose, effectively decomposing macromolecular polysaccharides into small molecular oligosaccharides, glucose or xylose. At the same time, the organic acids such as lactic acid and acetic acid produced in the fermentation process reduce the pH of the system to 4-5, and in this acidic environment, the connecting bonds (such as ester bonds and ether bonds) between lignin and carbohydrates are further destroyed, so that the originally tightly combined cellulose-hemicellulose-lignin network structure is disintegrated, forming a loose flocculent structure, creating an ideal precursor morphology for subsequent carbonization treatment. In order to obtain excellent fermentation effect, preferably, in step (1) of the present application, the bamboo is crushed and sieved through a 200-800 mesh sieve, and the concentration of lactococcus lactis solution is preferably 10 6 -10 8 CFU / mL, The weight ratio of bamboo powder to lactococcus lactis solution is preferably 1:0.2-1:2. The bamboo powder pretreated by lactic acid bacteria fermentation exhibits unique structural evolution characteristics during carbonization. The loose precursor structure allows volatile gases (CO, CO2, H2O, etc.) to escape more smoothly, and through the "bubble template effect", a large number of interconnected micropores (<2nm) and mesopores (2-50nm) are formed inside the material. This pretreatment method significantly improves the porosity of the material, which is usually 30-50% higher than that of the direct carbonization method. More importantly, the loose precursor structure effectively reduces the stress concentration during carbonization, avoids the collapse of the carbon skeleton, forms a continuous three-dimensional conductive network, greatly shortens the diffusion path of sodium ions, and significantly improves the ion transport performance of the hard carbon material.

[0008] In order to prevent the oxidation reaction, keep the integrity of the carbon structure, and also to inhibit the side reaction, reduce the impurity introduction, preferably, in the step (3) and the step (5) of the application, the inert atmosphere is nitrogen or argon.

[0009] In order to ensure the production efficiency, and at the same time avoid the structure rupture caused by the thermal stress of too fast heating, and the defect left by the uncontrolled volatilization, in the pre-carbonization treatment and the high-temperature carbonization forming process, the heating rate needs to be controlled, preferably, in the step (3) of the application, the heating rate is 5-15℃ / min to 400-600℃; in the step (5) of the application, the heating rate is 5-15℃ / min to 1200-1400℃.

[0010] Due to the adoption of the above technical solutions, the application has the following beneficial effects: 1、The bamboo-based hard carbon material prepared by the application shows excellent electrochemical performance as the negative electrode of the sodium ion battery, especially the hard carbon negative electrode prepared by using the bamboo powder fermented by the lactic acid bacteria for pretreatment, the first discharge capacity is more than 400mAh / g, and the capacity is still more than 310mAh / g after 20 times of charge-discharge cycles, which shows excellent capacity retention rate and cycle stability, and meets the application requirements of the high-performance sodium ion battery.

[0011] 2、The lactic acid bacteria fermentation pretreatment method adopted by the application has the advantages of environmental friendliness, low cost, simple operation and the like, can avoid the problems of high pollution and high energy consumption in the traditional chemical treatment method, and the method of the application is not only simple and easy to control, but also has good industrial production adaptability, and is very suitable for large-scale application. DETAILED DESCRIPTION

[0012] Figure 1 The XRD pattern of the hard carbon sodium ion battery negative electrode material obtained from the example 1 and the comparative example 1 of the application; Figure 2 The sodium ion battery electrochemical performance test graph of the hard carbon sodium ion battery negative electrode material obtained from the comparative example 2 of the application; Figure 3 The sodium ion battery electrochemical performance test graph of the hard carbon sodium ion battery negative electrode material obtained from the example 1 of the application; Figure 4 The sodium ion battery electrochemical performance test graph of the hard carbon sodium ion battery negative electrode material obtained from the comparative example 2 of the application. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application. Embodiment 1

[0014] A preparation method of a bamboo-based hard carbon sodium ion battery negative electrode material, comprising the following steps: (1) Bamboo powder pretreatment: fresh bamboo is sliced, pulverized and sieved (sieve mesh size is 500 mesh), dried, and bamboo powder is obtained, which is treated at 0.2 MPa steam pressure for 30 min to obtain bamboo powder; (2) Lactic acid bacteria fermentation pretreatment: the bamboo powder is mixed with lactococcus lactis liquid at a mass ratio of 1:1.1, the concentration of the lactococcus lactis liquid used is 10 8 CFU / mL, and fermentation is carried out at 45°C for 15 h in an anaerobic environment, so that the lactic acid bacteria secrete cellulase, hemicellulase and other biological enzymes to crack the glycosidic bond in the bamboo powder, and the organic acids such as lactic acid and acetic acid produced by metabolism further destroy the combination between cellulose-lignin structure, significantly improving the porosity and reactivity of the raw material. After fermentation, the bamboo powder precursor after fermentation pretreatment is obtained by repeatedly washing with deionized water until neutral (pH=7.4) and then drying at 80°C. (3) Pre-carbonization treatment: the bamboo powder precursor after fermentation pretreatment is placed in an inert atmosphere (nitrogen) protection, heated to 500°C at a heating rate of 10°C / min in a tube furnace, and kept at this temperature for 9 h to achieve preliminary carbonization, remove low molecular volatile substances and build a preliminary carbon skeleton structure. After natural cooling, a pre-carbonized sample is obtained; (4) Acid washing and impurity removal treatment: the pre-carbonized sample is soaked in a 1.5 mol / L hydrochloric acid (HCl) solution according to a solid-liquid ratio of 1g:20ml, and reacted at 70°C for 5h to remove inorganic impurities and metal residues, improve the purity and electrochemical stability of the carbon material. After acid washing, the sample is washed with deionized water until neutral (pH=6.9) and dried at 90°C for 9h to obtain a purified sample; (5) High-temperature carbonization forming: the purified sample is transferred into a high-temperature carbonization furnace, heated to 1300°C at a heating rate of 10°C / min under nitrogen atmosphere, and kept at the target temperature for 2h, which helps to form hard carbon material with moderate graphitization degree, large specific surface area, rich pore structure and good electrical conductivity. After carbonization, the sample is naturally cooled to obtain a bamboo-based hard carbon sodium ion battery negative electrode material, denoted as LABHC-S. The XRD pattern of the bamboo-based hard carbon sodium ion battery negative electrode material is shown in Figure 1 . Example 2

[0015] A preparation method of a bamboo-based hard carbon sodium ion battery negative electrode material, comprising the following steps: (1) Bamboo powder pretreatment: fresh bamboo is sliced, pulverized, and sieved (mesh size of 800 mesh), dried, and bamboo powder is obtained, which is treated at a steam pressure of 0.3 MPa for 20 min to obtain bamboo powder; (2) Lactic acid bacteria fermentation pretreatment: the bamboo powder is mixed with Lactococcus lactis liquid at a mass ratio of 1:2, and the concentration of the Lactococcus lactis liquid used is 10 6 CFU / mL, and in an anaerobic environment, it is incubated at 60°C for 6 h, so that the lactic acid bacteria secrete cellulase, hemicellulase and other biological enzymes to crack the glycosidic bond in the bamboo powder, and the lactic acid, acetic acid and other organic acids produced by metabolism further destroy the combination between cellulose-lignin structure, significantly improving the porosity and reactivity of the raw material. After fermentation, it is washed repeatedly with deionized water until neutral (pH=7.4), and then dried at 90°C (moisture content 5wt%), to obtain a bamboo powder precursor after fermentation pretreatment; (3) Pre-carbonization treatment: the bamboo powder precursor after fermentation pretreatment is placed in an inert atmosphere (nitrogen) protection, and heated to 600°C at a heating rate of 15°C / min in a tube furnace, and kept at this temperature for 6h to achieve preliminary carbonization, remove low molecular volatile substances and build a preliminary carbon skeleton structure. After natural cooling, a pre-carbonized sample is obtained; (4) Acid washing and impurity removal treatment: the pre-carbonized sample is soaked in a 2 mol / L hydrochloric acid (HCl) solution according to a solid-liquid ratio of 1g:30ml, and reacted at 90°C for 3h to remove inorganic impurities and metal residues, improve the purity and electrochemical stability of the carbon material. After acid washing, it is washed with deionized water until neutral (pH=7.5), and dried at 120°C for 6h to obtain a purified sample; (5) High-temperature carbonization forming: the purified sample is transferred into a high-temperature carbonization furnace, heated to 1400°C at a heating rate of 15 ℃ / min under nitrogen atmosphere, and kept at the target temperature for 1h, which helps to form a hard carbon material with moderate graphitization degree, large specific surface area, rich pore structure and good electrical conductivity. After carbonization, it is naturally cooled to obtain a bamboo-based hard carbon sodium ion battery negative electrode material, with a first discharge capacity of 398.4 mAh / g and a capacity of 305.9 mAh / g after 20 cycles. Example 3

[0016] A preparation method of a bamboo-based hard carbon sodium ion battery negative electrode material, comprising the following steps: (1) Bamboo powder pretreatment: Fresh bamboo was sliced, pulverized, and sieved (200 mesh screen), dried, and treated at 0.1 MPa steam pressure for 40 min to obtain bamboo powder; (2) Lactic acid bacteria fermentation pretreatment: Bamboo powder was mixed with Lactococcus lactis solution at a mass ratio of 1:0.2, and the concentration of the Lactococcus lactis solution was 10 8 CFU / mL. The lactic acid bacteria were incubated at 30°C for 24 h in an anaerobic environment to secrete cellulase and hemicellulase, which can break down the glycosidic bond in the bamboo powder. The lactic acid and acetic acid produced by the lactic acid bacteria can further destroy the combination between cellulose and lignin, significantly improving the porosity and reactivity of the raw material. After fermentation, the bamboo powder was washed with deionized water until it was neutral (pH = 7.1), and then dried at 70°C (moisture content 5wt%) to obtain the bamboo powder precursor after fermentation pretreatment; (3) Pre-carbonization treatment: The bamboo powder precursor after fermentation pretreatment was placed in a tube furnace under inert atmosphere (nitrogen) protection, and heated to 400°C at a heating rate of 5°C / min, and kept at this temperature for 12 h to achieve preliminary carbonization, remove low molecular volatile substances and build a preliminary carbon skeleton structure. After natural cooling, the pre-carbonized sample was obtained; (4) Acid washing and impurity removal: The pre-carbonized sample was soaked in 0.5 mol / L hydrochloric acid (HCl) solution at a solid-liquid ratio of 1g:25ml, and reacted at 50°C for 6h to remove inorganic impurities and metal residues, improve the purity and electrochemical stability of the carbon material. After acid washing, the sample was washed with deionized water until it was neutral (pH = 7.5), and then dried at 60°C for 12h to obtain a purified sample; (5) High-temperature carbonization molding: The purified sample was transferred to a high-temperature carbonization furnace, heated to 1200°C at a heating rate of 5°C / min under nitrogen atmosphere, and kept at the target temperature for 3h. This process helps to form a hard carbon material with moderate graphitization degree, large specific surface area, rich pore structure and good electrical conductivity. After carbonization, the sample was naturally cooled to obtain a bamboo-based hard carbon sodium ion battery negative electrode material with a first discharge capacity of 401.6 mAh / g and a capacity of 308.4 mAh / g after 20 cycles.

[0017] Comparative Example 1 (fermentation of raw bamboo powder) A method for preparing a bamboo-based hard carbon sodium ion battery negative electrode material, comprising the following steps: (1) Bamboo powder pretreatment: Fresh bamboo was sliced, pulverized, and sieved (500 mesh screen), dried, and treated at 0.1 MPa steam pressure for 40 min to obtain bamboo powder; (2) Lactic acid bacteria fermentation pretreatment: Bamboo powder was mixed with Lactococcus lactis solution at a mass ratio of 1:1.1, and the concentration of the Lactococcus lactis solution was 10 8CFU / mL, in an anaerobic environment, at 45℃, constant temperature fermentation for 15h, so that lactic acid bacteria secrete cellulase, hemicellulase and other biological enzymes, cleave the glycosidic bond in bamboo powder, and further destroy the combination between cellulose-lignin structure through the metabolism of lactic acid, acetic acid and other organic acids, significantly improve the porosity and reactivity of the raw material, after fermentation, repeatedly washed with deionized water to neutral (pH=7.4), and then dried at 80℃, to obtain the bamboo powder precursor after fermentation pretreatment; (3) Pre-carbonization treatment: the bamboo powder precursor after fermentation pretreatment is placed in an inert atmosphere (nitrogen) protection, heated to 500℃ at a heating rate of 10℃ / min in a tube furnace, and kept at this temperature for 9h to realize preliminary carbonization, remove low molecular volatile substances and build preliminary carbon skeleton structure, after natural cooling, the pre-carbonized sample is obtained; (4) Acid washing and impurity removal treatment: the pre-carbonized sample is soaked in 1.5mol / L hydrochloric acid (HCl) solution, reacted at 70℃ for 5h to remove inorganic impurities and metal residues, improve the purity and electrochemical stability of the carbon material, after acid washing, washed with deionized water to neutral (pH=6.9), and dried at 90℃ for 9h to obtain the purified sample; (5) High-temperature carbonization forming: the purified sample is transferred into a high-temperature carbonization furnace, heated to 1300℃ at a heating rate of 10℃ / min under nitrogen atmosphere, and kept at the target temperature for 2h, which helps to form hard carbon material with moderate graphitization degree, large specific surface area, rich pore structure and good electrical conductivity, after carbonization, natural cooling, finally obtain the bamboo-based hard carbon sodium ion battery negative material, recorded as LABHC-I, the XRD pattern of the bamboo-based hard carbon sodium ion battery negative material is shown in Figure 1 .

[0018] Comparative example 2 (cooked bamboo powder, without fermentation) A method for preparing a bamboo-based hard carbon sodium ion battery negative material, comprising the following steps: (1) Bamboo powder pretreatment: fresh bamboo is sliced, crushed and sieved (sieve mesh size is 500 mesh), dried to obtain dried bamboo powder, treated at 0.2MPa steam pressure for 30min to obtain bamboo powder; (2) Pre-carbonization treatment: the bamboo powder is placed in an inert atmosphere (nitrogen) protection, heated to 500℃ at a heating rate of 10℃ / min in a tube furnace, and kept at this temperature for 9h to realize preliminary carbonization, remove low molecular volatile substances and build preliminary carbon skeleton structure, after natural cooling, the pre-carbonized sample is obtained; (3) Pickling and impurity removal treatment: the pre-carbonized sample is immersed in a 1.5 mol / L hydrochloric acid (HCl) solution, and reacted at 70°C for 5h to remove inorganic impurities and metal residues, improve the purity and electrochemical stability of the carbon material, after pickling, the sample is washed with deionized water to neutral (pH = 6.9), and dried at 90°C for 9h to obtain a purified sample; (4) High-temperature carbonization forming: the purified sample is transferred into a high-temperature carbonization furnace, heated to 1300°C at a heating rate of 10°C / min under nitrogen atmosphere, and kept at the target temperature for 2h, which helps to form a hard carbon material with moderate graphitization degree, large specific surface area, rich pore structure and good electrical conductivity, after carbonization, the sample is naturally cooled, and finally a bamboo-based hard carbon sodium ion battery negative electrode material is obtained, denoted as BHC. Performance test:

[0019] To verify the influence of different preparation processes in the application on the electrochemical performance of the bamboo-based hard carbon sodium ion battery negative electrode material, the hard carbon materials prepared in Example 1 (LABHC-S), Comparative Example 1 (LABHC-I), and Comparative Example 2 (BHC) were selected as the negative active material, and 2032 type button sodium ion batteries were assembled, and the electrochemical performance was tested under constant current charge and discharge mode, and the test voltage range was 0.01-2.0V (vs. Na + / Na), and the test results are as follows: The first discharge capacity of LABHC-S (Example 1) is more than 400 mAh / g, and the capacity after 20 charge and discharge cycles is more than 310 mAh / g, as shown in Figure 3 and Table 1; The first discharge capacity of LABHC-I (Comparative Example 1) is more than 380 mAh / g, and the capacity after 20 charge and discharge cycles is more than 290 mAh / g, as shown in Figure 2 and Table 1; The first discharge capacity of BHC (Comparative Example 2) is about 350 mAh / g, and the capacity after 20 charge and discharge cycles is about 270 mAh / g, as shown in Figure 4 and Table 1.

[0020] Table 1 Performance of different sodium ion battery negative electrode materials Sample Type of raw material Pre-treatment method Initial discharge capacity (mAh / g) Capacity after 20 cycles (mAh / g) Capacity retention rate (%) BHC Raw bamboo powder Direct carbonization 306.9 160.9 52.4 LABHC-I Raw bamboo powder Lactic acid bacteria fermentation 350.7 260.3 74.2 LABHC-S Cooked bamboo powder Lactic acid bacteria fermentation 402.2 310.4 77.2 From the above results, it can be seen that the bamboo-based hard carbon materials (LABHC-I, LABHC-S) prepared by lactic acid bacteria fermentation pretreatment exhibit higher initial specific capacity and better cycle stability than the comparative material (BHC), showing excellent sodium ion storage performance. Especially, LABHC-S prepared by lactic acid bacteria fermentation treatment using cooked bamboo powder as raw material, its capacity retention rate and reversibility are the most outstanding, indicating that the lactic acid bacteria fermentation of cooked bamboo powder can significantly improve the microstructure and pore distribution of the precursor, effectively improve the electrochemical activity and sodium ion intercalation / deintercalation performance of the carbon material.

[0021] It is worth noting that the method for preparing bamboo-based hard carbon negative material by lactic acid bacteria fermentation pretreatment described in the present application is not limited to the specific process parameters shown in the above examples. Without departing from the core technical idea of the present application, those skilled in the art can optimize and adjust the process conditions such as lactic acid bacteria species, fermentation temperature and time, fermentation liquid concentration, carbonization temperature and heating rate, etc. according to the characteristics of different raw materials and application requirements, and can also try to introduce other types of biological pretreatment methods or composite carbon source systems to further improve the material performance. The above adjustments all belong to the reasonable extension of the present application and should also be included in the protection scope of the present patent.

Claims

1. A method for preparing a bamboo-based hard carbon sodium-ion battery anode material, characterized in that, Includes the following steps: (1) Bamboo powder pretreatment: Fresh bamboo is sliced, crushed, sieved and dried to obtain dried bamboo powder, which is then treated under a steam pressure of 0.1-0.3 MPa for 20-40 min to obtain bamboo powder; (2) Pretreatment of lactic acid bacteria fermentation: Bamboo powder is mixed with lactococcus lactis solution and fermented in a constant temperature incubator under anaerobic conditions. The fermentation temperature is controlled at 30-60℃ and the fermentation time is 6-24 h. After fermentation, the mixture is washed with deionized water until neutral and then dried. (3) Pre-carbonization treatment: Place the bamboo powder after fermentation treatment in step (2) in an inert atmosphere, heat it to 400-600 ℃, keep it at a constant temperature for 6-12 h, and obtain the pre-carbonized sample after cooling. (4) Acid washing to remove impurities: Immerse the pre-carbonized sample obtained in step (3) in 0.5-2 mol / L hydrochloric acid solution and react continuously at 50-90 ℃ for 3-6 h. Then wash thoroughly with deionized water until neutral and dry at 60-120 ℃ for 6-12 h. (5) High-temperature carbonization molding: The material after acid washing and drying in step (4) is heated to 1200-1400℃ in an inert atmosphere and carbonized at a constant temperature for 1-3 h. After cooling, the final sodium-ion battery anode material is obtained.

2. The method for preparing bamboo-based hard carbon sodium-ion battery anode material as described in claim 1, characterized in that: In step (1), the sample is passed through a 200-800 mesh sieve.

3. The method for preparing bamboo-based hard carbon sodium-ion battery anode material as described in claim 1, characterized in that: In step (2), the concentration of the Lactococcus lactis solution is 10. 6 -10 8 CFU / mL.

4. The method for preparing the bamboo-based hard carbon sodium-ion battery anode material as described in claim 1, characterized in that: In step (2), the weight ratio of bamboo powder to lactococcus lactis solution is 1:0.2-1:

2.

5. The method for preparing the bamboo-based hard carbon sodium-ion battery anode material as described in claim 1, characterized in that: In steps (3) and (5), the inert atmosphere is nitrogen or argon.

6. The method for preparing the bamboo-based hard carbon sodium-ion battery anode material as described in claim 1, characterized in that: In step (3), the temperature is increased to 400-600 ℃ at a heating rate of 5-15 ℃ / min.

7. The method for preparing the bamboo-based hard carbon sodium-ion battery anode material as described in claim 1, characterized in that: In step (5), the temperature is increased to 1200-1400℃ at a heating rate of 5-15℃ / min.

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