A biomass hard carbon anode material, its preparation method and application

Abstract

This invention belongs to the field of anode material technology and discloses a biomass hard carbon anode material and its preparation method and application. The steps include: (1) culturing soybean rhizobium in a culture medium; (2) washing, drying, and pulverizing the soybean rhizobium to obtain soybean rhizobium powder; (3) pre-carbonizing the soybean rhizobium powder, followed by high-temperature carbonization and crushing; (4) acid leaching the product, and then obtaining a biomass hard carbon anode material after post-treatment. This invention, by using a biomass precursor to prepare biomass hard carbon material, can achieve uniform nitrogen doping, and further improve the electrochemical performance of the material by controlling the preparation process conditions, possessing broad market application prospects; at the same time, the preparation method of this invention is simple and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of anode material preparation technology, specifically to a biomass hard carbon anode material and its preparation method and application. Background Technology

[0002] With the rapid development of modern technology, the demand for electrochemical energy storage devices, represented by lithium-ion batteries, is increasing daily. However, the scarcity of lithium resources on Earth leads to significant price fluctuations. Sodium, on the other hand, is the fourth most abundant element in the Earth's crust, widely distributed and unrestricted by resources or location. Furthermore, sodium-ion batteries offer better safety performance and a service life comparable to lithium-ion batteries, making their application prospects very broad. The positive and negative electrode materials are the core of sodium-ion battery operation; they are not only key to improving performance but also the main way to solve the cost bottleneck. Common negative electrode materials for sodium-ion batteries include alloy-type, conversion-type, and intercalation-type materials. Compared to alloy-type and conversion-type materials, intercalation-type materials exhibit better performance during charging and discharging. + Carbon-based materials exhibit low lattice volume expansion during insertion and extraction, demonstrating good structural integrity and cycle stability, as well as higher initial coulombic efficiency and higher rate performance. As a representative of intercalation materials, carbon-based materials are considered the most promising anode materials for sodium-ion batteries due to their abundant resources and environmental friendliness.

[0003] Carbon-based materials are classified into four categories based on the arrangement of carbon atoms: graphite, graphene, soft carbon, and hard carbon. Hard carbon anode materials, with their low sodium storage potential, high specific capacity, and wide availability, are a key focus of research in sodium-ion battery anode materials. Researchers have developed a series of hard carbon anode materials based on carbon-containing raw materials such as pitch-based, biomass-based, and resin-based materials. Biomass materials have attracted significant attention due to their unique advantages, such as abundant and readily available raw material sources, high carbon yield, environmental friendliness, and the presence of multiple elements, making them a promising precursor for sodium-ion battery anode materials.

[0004] However, hard carbon anode materials still face challenges in commercial applications, such as low initial coulombic efficiency, poor rate performance, and poor cycle stability. To address these issues, researchers have adopted several solutions, including adjusting interlayer spacing, elemental doping, and optimizing pore structure. For example, CN202110783054.X discloses a nitrogen-doped hard carbon anode material, its preparation method, and its application. This material is obtained through primary purification, secondary purification, calcination, and plasma treatment. The biomass raw materials include grapefruit peel, durian shell, coconut shell, almond, corn cob, shrimp shell, onion, soybean, shiitake mushroom, and orchid leaves. The resulting hard carbon anode material exhibits large interlayer spacing, high porosity, and large specific surface area. However, its initial coulombic efficiency is low, and the excessively large specific surface area is not conducive to forming a high-quality solid electrolyte interphase (SEI) film. The morphological uniformity of this hard carbon anode material is also poor, and the process is complex, requiring high-energy-consuming and highly polluting ammonia plasma treatment, which may cause atmospheric pollution.

[0005] In summary, it is crucial to develop a fast, efficient, and uniform nitrogen-doped hard carbon anode material and its preparation method, so that the material has a uniform surface morphology, high capacity, high initial efficiency, and long cycle life, and its preparation method is environmentally friendly and energy-efficient. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a biomass hard carbon anode material, its preparation method and application, aiming to solve the problems of uneven nitrogen doping, low initial coulombic efficiency, poor uniformity of material surface morphology, complex process and high energy consumption and high pollution of current hard carbon anode materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first objective of this invention is to provide a biomass hard carbon anode material, wherein the biomass precursor of the biomass hard carbon anode material is soybean rhizobium. By adopting the above technical solution, soybean rhizobium can fix the surrounding free nitrogen through nitrogen fixation, thereby achieving uniform and stable nitrogen doping, resulting in a biomass hard carbon anode material with uniform nitrogen doping, good morphological uniformity, and high initial efficiency.

[0009] The second objective of this invention is to provide a method for preparing the aforementioned biomass hard carbon anode material. This method utilizes bioculture technology to achieve uniform nitrogen doping, combines a pre-carbonization process to introduce more oxygen-containing functional groups, and removes impurity metal elements through acid washing. This preparation method is simple, low-cost, and environmentally friendly, making it suitable for industrial production. The preparation method includes the following steps:

[0010] (1) Cultivate soybean rhizobia in a culture medium;

[0011] (2) The soybean rhizobium obtained in step (1) is washed, dried and pulverized to obtain soybean rhizobium powder.

[0012] (3) The soybean rhizobium powder obtained in step (2) is pre-carbonized. After pre-carbonization, it is taken out, cleaned with solvent and dried. Then it is subjected to high-temperature carbonization and crushing to obtain black powder product.

[0013] (4) The black powder product obtained in step (3) is subjected to acid leaching to remove soluble metal elements such as potassium, calcium, and magnesium from the material, and then post-processed to obtain biomass hard carbon anode material.

[0014] Preferably, in step (1), the soybean rhizobium culture medium is yeast mannitol agar (YMA), and the composition of the YMA liquid culture medium (1L) is: 10.0g mannitol, 0.2-0.8g yeast extract (as a nitrogen source), 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L. By using the culture medium, yeast extract, as an amino acid source, contains group B vitamins and rhizobium growth factors, which can promote the growth of rhizobia.

[0015] Preferably, in step (1), the shaking speed is 150-250 r / min, and the temperature is constant at 28℃. By using this temperature, the growth rate of soybean rhizobia can be maximized.

[0016] Preferably, in step (1), the size of the soybean rhizobium colony is not less than 1 cm.

[0017] Preferably, in step (2), the cultured rhizobium is first separated from the liquid using a centrifuge. The separated solid is placed in an analytical grade formaldehyde solution and mechanically stirred to remove residual culture medium. The mass ratio of formaldehyde solution to solid is 1:2 to 1:6. After stirring thoroughly, the mixture is centrifuged and then washed with ethanol or isopropanol solution. After separating the solid, it is dried at a temperature of 60 to 100°C for 6 to 24 hours.

[0018] Furthermore, the centrifuge speed is 5000–8000 r / min, and the centrifugation time is 2–5 min. The stirrer speed is 150–500 r / min, and the stirring time is 0.5–2 h.

[0019] Preferably, in step (2), the soybean rhizobium is pulverized by a cell wall breaker, and more preferably, the pulverized material can pass through a 200-mesh sieve, i.e., the particle size is less than 0.074 mm.

[0020] Preferably, in step (3), the pre-carbonization treatment is specifically a hydrothermal method, with a treatment time of 6–20 h, a temperature of 150–400 °C, and a material-to-liquid mass-to-volume ratio (mass of solid material to volume of liquid) of 1:2–1:4. By employing hydrothermal treatment, more oxygen can be introduced while simultaneously resulting in a smaller pore size (approximately 2–6 nm) in the material, further enhancing its initial efficiency.

[0021] Preferably, in step (3), the pre-carbonized solid product is taken out and cleaned. The cleaning solvent is one or more of water and alcohol solvents, and more preferably, the alcohol solvent is selected from at least one of ethanol and isopropanol.

[0022] Preferably, in step (3), the drying temperature is 60-100℃ and the drying time is 6-24h.

[0023] Preferably, in step (3), the high-temperature carbonization treatment is specifically tube furnace sintering, with a heating rate of 5-10℃ / min, a constant temperature of 700-1500℃, a constant temperature carbonization time of 4-10h, and the high-temperature carbonization atmosphere is an inert atmosphere, more preferably at least one of argon and helium.

[0024] Preferably, in step (3), the crushing process is ball milling, with a ball milling speed of 300-800 r / min and a ball milling time of 0.5-4 h, to obtain uniform particles with a particle size of 0.5-15 μm.

[0025] Preferably, in step (4), the acid leaching treatment involves soaking and stirring in a 1-5 mol / L hydrochloric acid solution for 1-5 hours at a stirring speed of 150-500 r / min.

[0026] Preferably, in step (4), the post-processing includes: filtering the soaked solution to separate the solid powder, washing it with deionized water, and drying it to obtain the biomass hard carbon anode material. More preferably, the drying temperature is 60–100°C, and the drying time is 6–24 h.

[0027] The third objective of this invention is to provide an application of a biomass hard carbon anode material in sodium-ion batteries. This biomass hard carbon anode material, when used as an anode active material in sodium-ion batteries, has the characteristics of high specific capacity, high initial coulombic efficiency, and stable cycle performance.

[0028] Based on the above technical solution, the present invention has the following beneficial effects:

[0029] (1) In this invention, adding yeast powder to the culture medium of soybean rhizobium can serve as a nitrogen source, thereby increasing the nitrogen content of soybean rhizobium and making it more evenly distributed.

[0030] (2) In this invention, the pre-carbonization process can introduce more oxygen-containing functional groups while fixing the carbon skeleton, that is, while maintaining a good surface morphology, it can also provide more Na due to the more oxygen-containing functional groups. + Adsorption sites can significantly improve the specific capacity of hard carbon materials.

[0031] (3) In this invention, the acid washing process can effectively remove soluble impurity metal elements such as potassium, calcium, and magnesium from hard carbon anode materials.

[0032] (4) By using biomass precursors to prepare biomass hard carbon materials, the present invention can achieve uniform nitrogen doping and further improve the electrochemical performance of the materials by controlling the preparation process conditions, which has broad market application prospects; at the same time, the preparation method of the present invention is simple and suitable for large-scale industrial production. Attached Figure Description

[0033] Figure 1 The first charge-discharge curve of the sodium-ion battery assembled with the hard carbon anode material prepared in Comparative Example 1.

[0034] Figure 2 The constant current cycling curve of the sodium-ion battery assembled with the hard carbon anode material prepared in Comparative Example 1.

[0035] Figure 3 The XPS spectrum of the hard carbon anode material C1s prepared in Comparative Example 1 is shown.

[0036] Figure 4 The first charge-discharge curve of a sodium-ion battery assembled with the hard carbon anode material prepared in Example 1;

[0037] Figure 5 The constant current cycling curve of a sodium-ion battery assembled with the hard carbon anode material prepared in Example 1;

[0038] Figure 6 The image shows the XPS spectrum of the hard carbon anode material C1s prepared in Example 1.

[0039] Figure 7 This is a SEM image of the hard carbon anode material prepared in Example 1.

[0040] Figure 8 This is a comparison chart of the rate performance of Example 1, Example 3, Comparative Example 1, and Comparative Example 2.

[0041] Figure 9 This is the isothermal adsorption-desorption curve of Example 1. Detailed Implementation

[0042] This invention provides a biomass hard carbon anode material, its preparation method, and its application. To better clarify and understand the purpose, process scheme, and advantages of this invention, specific embodiments and accompanying drawings are provided below to further describe the technical solution and implementation methods of this invention clearly, completely, and in detail. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solution of this invention, providing detailed implementation methods and specific operating procedures, but these are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, and instruments used in the embodiments, unless otherwise specified, can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention can all achieve the reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0044] Example 1:

[0045] A biomass hard carbon anode material and its specific preparation steps are as follows:

[0046] (1) The composition of yeast mannitol agar (YMA) liquid medium (1L) was as follows: 10.0g mannitol, 0.8g yeast extract (as nitrogen source), 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L. Soybean rhizobia were inoculated into YMA medium and cultured at 170r / min in a shaker at 28℃ for 48h.

[0047] (2) The cultured rhizobia were separated from the liquid using a centrifuge at 5000 rpm for 5 minutes. The separated solid was then mechanically stirred with analytical grade formaldehyde solution at 150 rpm for 2 hours. The mass-to-volume ratio of formaldehyde solution to solid was 1:4. After thorough stirring, the mixture was centrifuged at 5000 rpm for 2 minutes. After centrifugation, the mixture was washed with ethanol. The separated solid was then dried in an oven at 60°C for 24 hours. After drying, the solid was crushed into powder using a high-speed blender for 3 minutes.

[0048] (3) Place the powder in a hydrothermal reactor using deionized water as the solvent, with a material-to-liquid mass-to-volume ratio of 1:2. Place the reactor in a hydrothermal oven at 180℃ for 12 hours. After hydrothermal treatment, remove the reactor and filter to separate the solid. Place the separated solid in anhydrous ethanol, stir manually until homogeneous, and continue filtration, repeating this process three times. Place the final solid in a 60℃ oven and dry for 24 hours to obtain a fluffy powder. Place the powder in a ceramic boat, level it, and place it in a tube furnace. Under argon atmosphere, heat at a rate of 5℃ / min, maintain the temperature at 700℃ for 10 hours. Place the obtained product in a ball mill for crushing at a speed of 800 r / min for 0.5 hours.

[0049] (4) The crushed powder was soaked and stirred in a 1 mol / L hydrochloric acid solution for 5 h at a stirring speed of 150 r / min. The solid was separated from the stirred solution by vacuum filtration and washed with deionized water until pH=7. The washed solid was dried in an oven at 60℃ for 24 h to obtain hard carbon anode material.

[0050] The obtained hard carbon negative electrode material, conductive carbon black and binder PVDF were mixed evenly at a mass ratio of 8:1:1, and an appropriate amount of NMP was added as a solvent and stirred evenly. The above slurry was evenly coated on an aluminum sheet with a thickness of 150 mm. Then, the electrode was placed in an 80℃ vacuum oven to dry for 8 hours and then compacted to make a negative electrode sheet. CR2303 button cells were assembled in an argon-filled glove box, using glass fiber Whatman GF / D as the separator, 1 mol / L NaPF6 DEC:EC:PC = 1:1:1 as the electrolyte, and a sodium metal sheet as the reference electrode.

[0051] The assembled coin cells were tested at 30°C, with a current density of 0.03 A / g for the first three cycles, and a subsequent cycle current density of 0.2 A / g. Figure 4 As shown, the battery's initial coulombic efficiency is 86%. Figure 5 As shown, the specific capacity after 200 cycles is 176 mA h / g. The XPS spectrum of C1 s is as follows. Figure 6 As shown, the proportions of CO / CN and C=O functional groups are 22.4% and 24.5%, respectively.

[0052] Example 2:

[0053] A biomass hard carbon anode material and its specific preparation steps are as follows:

[0054] (1) The composition of yeast mannitol agar (YMA) liquid medium (1L) was as follows: 10.0g mannitol, 0.6g yeast extract (as nitrogen source), 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L. Soybean rhizobia were inoculated into YMA medium and cultured at 150r / min in a shaker at 28℃ for 36h.

[0055] (2) The cultured rhizobia were separated from the liquid using a centrifuge at 5000 rpm for 5 minutes. The separated solid was then mechanically stirred with analytical grade formaldehyde solution at 200 rpm for 1 hour. The mass-to-volume ratio of formaldehyde solution to solid was 1:2. After thorough stirring, the mixture was centrifuged at 5000 rpm for 5 minutes. After centrifugation, the mixture was washed with isopropanol. The separated solid was then dried in an oven at 100°C for 6 hours. After drying, the solid was crushed into powder using a high-speed blender for 3 minutes.

[0056] (3) Place the powder in a hydrothermal reactor using deionized water as the solvent, with a material-to-liquid mass-to-volume ratio of 1:4. Place the reactor in a hydrothermal oven at 400℃ for 6 hours. After hydrothermal treatment, remove the reactor and filter to separate the solid. Place the separated solid in anhydrous ethanol, stir manually until homogeneous, and continue filtration, repeating this process three times. Place the final solid in a 100℃ oven and dry for 6 hours to obtain a fluffy powder. Place the powder in a ceramic boat, level it, and place it in a tube furnace. Under argon atmosphere, heat at a rate of 5℃ / min, maintain the temperature at 1100℃ for 6 hours. Place the obtained product in a ball mill for crushing at a speed of 500 r / min for 1 hour.

[0057] (4) The crushed powder was soaked and stirred in a 2 mol / L hydrochloric acid solution for 1 h at a stirring speed of 300 r / min. The solid was separated from the stirred solution by vacuum filtration and washed with deionized water until pH=7. The washed solid was dried in an oven at 80℃ for 12 h to obtain hard carbon anode material.

[0058] The obtained hard carbon anode material was assembled into a battery according to the method in Example 1.

[0059] The assembled coin cells were tested at 30°C, with a current density of 0.03 A / g for the first three cycles, followed by a current density of 0.2 A / g. After 200 cycles, the specific capacity was 134 mA h / g, and the initial coulombic efficiency was 70%.

[0060] Example 3:

[0061] A biomass hard carbon anode material and its specific preparation steps are as follows:

[0062] (1) The composition of yeast mannitol agar (YMA) liquid medium (1L) was as follows: 10.0g mannitol, 0.6g yeast extract (as nitrogen source), 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L. Soybean rhizobia were inoculated into YMA medium and cultured at 170r / min in a shaker at 28℃ for 36h.

[0063] (2) The cultured rhizobia were separated from the liquid using a centrifuge at 8000 rpm for 2 minutes. The separated solid was then mechanically stirred with analytical grade formaldehyde solution at 500 rpm for 0.5 hours. The mass-to-volume ratio of formaldehyde solution to solid was 1:4. After thorough stirring, the mixture was centrifuged at 5000 rpm for 2 minutes. After centrifugation, the mixture was washed with ethanol and the separated solid was dried in an oven at 60°C for 24 hours. After drying, the solid was crushed into powder using a high-speed blender for 3 minutes.

[0064] (3) Place the powder in a hydrothermal reactor using deionized water as the solvent, with a material-to-liquid mass-to-volume ratio of 1:2. Place the reactor in a hydrothermal oven at 150℃ for 20 hours. After hydrothermal treatment, remove the reactor and filter to separate the solid. Place the separated solid in anhydrous ethanol, stir manually until homogeneous, and continue filtration, repeating this process three times. Place the final solid in a 100℃ oven and dry for 6 hours to obtain a fluffy powder. Place the powder in a ceramic boat, level it, and place it in a tube furnace. Under argon atmosphere, heat at a rate of 5℃ / min, maintain the temperature at 1500℃ for 4 hours. Place the obtained product in a ball mill for crushing at a speed of 500 r / min for 1 hour.

[0065] (4) The crushed powder was soaked and stirred in a 5 mol / L hydrochloric acid solution for 1 h at a stirring speed of 500 r / min. The solid was separated from the stirred solution by vacuum filtration and washed with deionized water until pH=7. The washed solid was dried in an oven at 100℃ for 6 h to obtain hard carbon anode material.

[0066] The obtained hard carbon anode material was assembled into a battery according to the method in Example 1.

[0067] The assembled coin cells were tested at 30°C, with a current density of 0.03 A / g for the first three cycles, followed by a current density of 0.2 A / g. After 200 cycles, the specific capacity was 153 mA h / g, and the initial coulombic efficiency was 76%.

[0068] Comparative Example 1:

[0069] A biomass hard carbon anode material and its specific preparation steps are as follows:

[0070] (1) The composition of yeast mannitol agar (YMA) liquid medium (1L) was as follows: 10.0g mannitol, 0.2g yeast extract (as nitrogen source), 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L. Soybean rhizobia were inoculated into YMA medium and cultured at 250r / min in a shaker at 28℃ for 36h.

[0071] (2) The cultured rhizobia were separated from the liquid using a centrifuge at 5000 rpm for 5 minutes. The separated solid was then mechanically stirred with analytical grade formaldehyde solution at 150 rpm for 2 hours. The mass-to-volume ratio of formaldehyde solution to solid was 1:4. After thorough stirring, the mixture was centrifuged at 5000 rpm for 5 minutes. After centrifugation, the mixture was washed with ethanol and the separated solid was dried in an oven at 60°C for 24 hours. After drying, the solid was crushed into powder using a high-speed blender for 3 minutes.

[0072] (3) Place the powder in a hydrothermal reactor using deionized water as the solvent, with a material-to-liquid mass-to-volume ratio of 1:2. Place the reactor in a hydrothermal oven at 180℃ for 12 hours. After hydrothermal treatment, remove the reactor and filter to separate the solid. Place the separated solid in anhydrous ethanol, stir manually until homogeneous, and continue filtration, repeating this process three times. Place the final solid in a 60℃ oven and dry for 24 hours to obtain a fluffy powder. Place the powder in a ceramic boat, level it, and place it in a tube furnace. Introduce an argon atmosphere, raise the temperature at a rate of 5℃ / min, maintain the temperature at 700℃ for 10 hours, and then grind the product in a ball mill at a speed of 300 r / min for 4 hours.

[0073] (4) The crushed powder was soaked and stirred in a 1 mol / L hydrochloric acid solution for 5 hours at a stirring speed of 150 r / min. The solid was separated from the stirred solution by vacuum filtration and washed with deionized water until pH=7. The washed solid was dried in a 60℃ oven for 12 hours to obtain hard carbon anode material.

[0074] The obtained hard carbon anode material was assembled into a battery according to the method in Example 1.

[0075] The assembled coin cells were tested at 30°C, with a current density of 0.03 A / g for the first three cycles, and a subsequent cycle current density of 0.2 A / g. Figure 1 As shown, the battery's initial coulombic efficiency is 63%. Figure 2 As shown, the specific capacity after 200 cycles is 96 mA h / g. The XPS spectrum of C1 s is as follows. Figure 3 As shown, the proportions of CO / CN and C=O functional groups are 14.5% and 20.4%, respectively. Compared with Example 1, it can be seen that changing the amount of yeast powder significantly affects the electrochemical performance.

[0076] Comparative Example 2:

[0077] A biomass hard carbon anode material and its specific preparation steps are as follows:

[0078] (1) The composition of yeast mannitol agar (YMA) liquid medium (1L) was as follows: 10.0g mannitol, 0.2g yeast extract (as nitrogen source), 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L. Soybean rhizobia were inoculated into YMA medium and cultured at 170r / min in a shaker at 28℃ for 36h.

[0079] (2) The cultured rhizobia were separated from the liquid using a centrifuge at 5000 rpm for 5 minutes. The separated solid was then mechanically stirred with analytical grade formaldehyde solution at 150 rpm for 2 hours. The mass-to-volume ratio of formaldehyde solution to solid was 1:4. After thorough stirring, the mixture was centrifuged at 5000 rpm for 2 minutes. After centrifugation, the mixture was washed with ethanol. The separated solid was then dried in an oven at 60°C for 24 hours. After drying, the solid was crushed into powder using a high-speed blender for 3 minutes.

[0080] (3) Place the powder into a ceramic boat, shake it to level it, and place it into a tube furnace. Introduce an argon atmosphere, raise the temperature at a rate of 5℃ / min, hold it at 700℃ for 10 hours. Place the resulting product into a ball mill for crushing. The ball milling speed is 800 r / min, and the ball milling time is 0.5 hours.

[0081] (4) The crushed powder was soaked and stirred in a 1 mol / L hydrochloric acid solution for 5 hours at a stirring speed of 150 r / min. The solid was separated from the stirred solution by vacuum filtration and washed with deionized water until pH=7. The washed solid was dried in an oven at 70℃ for 18 hours to obtain hard carbon anode material.

[0082] The obtained hard carbon anode material was assembled into a battery according to the method in Example 1.

[0083] The assembled coin cells were tested at 30°C, with a current density of 0.03 A / g for the first three cycles, followed by a current density of 0.2 A / g. After 200 cycles, the specific capacity was 77 mA h / g, and the initial coulombic efficiency was 45%.

[0084] Comparative Example 3:

[0085] A biomass hard carbon anode material and its specific preparation steps are as follows:

[0086] (1) The composition of yeast mannitol agar (YMA) liquid medium (1L) was: 10.0g mannitol, 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L. Soybean rhizobia were inoculated into YMA medium and cultured at 170r / min in a shaker at 28℃ for 36h.

[0087] (2) The cultured rhizobia were separated from the liquid using a centrifuge at 5000 rpm for 5 minutes. The separated solid was then mechanically stirred with analytical grade formaldehyde solution at 150 rpm for 2 hours. The mass-to-volume ratio of formaldehyde solution to solid was 1:4. After thorough stirring, the mixture was centrifuged at 5000 rpm for 2 minutes. After centrifugation, the mixture was washed with ethanol. The separated solid was then dried in an oven at 60°C for 24 hours. After drying, the solid was crushed into powder using a high-speed blender for 3 minutes.

[0088] (3) Place the powder into a porcelain boat, level it, and place it in a tube furnace for air sintering. The heating rate is 5℃ / min, the holding temperature is 400℃, and the holding time is 4h. Without waiting for cooling, argon gas is directly introduced, the heating rate is 5℃ / min, the holding temperature is 700℃, and the holding time is 10h. The obtained product is then placed in a ball mill for crushing. The ball milling speed is 800r / min, and the ball milling time is 0.5h.

[0089] (4) The crushed powder was soaked and stirred in a 1 mol / L hydrochloric acid solution for 5 hours at a stirring speed of 150 r / min. The solid was separated from the stirred solution by vacuum filtration and washed with deionized water until pH=7. The washed solid was dried in an oven at 60℃ for 6 hours to obtain hard carbon anode material.

[0090] The obtained hard carbon anode material was assembled into a battery according to the method in Example 1.

[0091] The assembled coin cells were tested at 30°C, with a current density of 0.03 A / g for the first three cycles, followed by a current density of 0.2 A / g. After 200 cycles, the specific capacity was 56 mA h / g, and the initial coulombic efficiency was 37%. A comparison with the example shows that the absence of yeast powder and the use of incorrect pretreatment methods significantly reduced the electrochemical performance.

[0092] The specific surface area, average pore size, and interlayer spacing of the materials obtained in Examples 1-3 and Comparative Examples 1-3 were tested, and the specific parameters are shown in Table 1.

[0093] Table 1 Summary of structural parameters of materials in the examples and comparative examples

[0094]

[0095] The batteries obtained in Examples 1-3 and Comparative Examples 1-3 were tested for their initial coulombic efficiency and discharge capacity after 200 cycles. The results further demonstrate that the sodium-ion batteries using the hard carbon negative electrode sheet of this application maintain a high charge and discharge capacity after cycling. See Table 2 for details.

[0096] Table 2 Summary of Electrochemical Performance of Examples and Comparative Materials

[0097]

[0098] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for preparing a biomass hard carbon anode material, characterized in that: The steps include the following: (1) Cultivate soybean rhizobia in a culture medium; the culture medium is yeast mannitol agar; (2) Soybean rhizobium is washed, dried and pulverized to obtain soybean rhizobium powder; (3) The soybean rhizobium powder was pre-carbonized by hydrothermal method, followed by high-temperature carbonization and crushing. (4) The product is subjected to acid leaching treatment, followed by post-treatment to obtain biomass hard carbon anode material.

2. The method for preparing a biomass hard carbon anode material according to claim 1, characterized in that: The culture medium consisted of: 10.0g mannitol, 0.2-0.8g yeast extract, 0.4g K2HPO4, 0.2g MgSO4·7H2O, 0.1g CaCl2·H2O, 0.1g NaCl, 4mL Rh trace element solution, and ddH2O to a final volume of 1L.

3. The method for preparing a biomass hard carbon anode material according to claim 1, characterized in that: In step (2), the powder is pulverized and then passed through a 200-mesh sieve.

4. The method for preparing a biomass hard carbon anode material according to claim 1, characterized in that: In step (3), the hydrothermal treatment time is 6 to 20 hours, the temperature is 150 to 400°C, and the mass-to-volume ratio of the liquid to the material is 1:2 to 1:

4.

5. The method for preparing a biomass hard carbon anode material according to claim 1, characterized in that: In step (3), the heating rate of the high-temperature carbonization treatment is 5-10℃ / min, the constant temperature is 700-1500℃, the carbonization time is 4-10h, and the high-temperature carbonization atmosphere is argon.

6. The method for preparing a biomass hard carbon anode material according to claim 1, characterized in that: In step (3), the crushing process is specifically ball milling, with a ball milling speed of 300-800 r / min and a ball milling time of 0.5-4 h.

7. The method for preparing a biomass hard carbon anode material according to claim 1, characterized in that: In step (4), the acid leaching treatment involves soaking and stirring in a 1-5 mol / L hydrochloric acid solution for 1-5 hours at a stirring speed of 150-500 r / min.

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

9. The application of a biomass hard carbon anode material prepared by any one of the preparation methods of claims 1-7 in a sodium-ion battery.

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