Biomass-based porous carbon and preparation method thereof, silicon-carbon negative electrode material and preparation method thereof

Abstract

The application provides a biomass-based porous carbon and a preparation method thereof, and a silicon-carbon negative electrode material and a preparation method thereof, and relates to the field of secondary battery negative electrode materials. The preparation method of the biomass-based porous carbon comprises the following steps: mixing a biomass raw material and urea to obtain pretreated material; mixing the pretreated material with a fermentation agent and performing stack aerobic fermentation; drying fermentation products obtained through fermentation to obtain a pre-pore precursor; performing carbonization treatment on the pre-pore precursor in an inert atmosphere to obtain carbonization products; and introducing activating gas into the carbonization products to perform activation treatment, thereby obtaining the biomass-based porous carbon. The fermentation treatment and the activation treatment are combined in the application, and the pore structure of the porous carbon material is synergistically regulated. The biomass-based porous carbon prepared by the method of the application has a high specific surface area, a pore structure suitable for silane deposition and good surface chemical properties, and the silicon-carbon negative electrode material prepared from the material has excellent electrochemical performance.

Description

Technical Field

[0001] This application relates to the field of secondary battery anode materials, and in particular to a biomass-based porous carbon and its preparation method, and a silicon-carbon anode material and its preparation method. Background Technology

[0002] Porous carbon materials, due to their high specific surface area, tunable pore structure, good chemical stability, and conductivity, are widely used in supercapacitors, lithium-ion batteries, adsorption separation, and catalyst supports. In recent years, in the field of lithium-ion battery anode materials, using porous carbon as a support and loading silicon through chemical vapor deposition (CVD) to construct silicon-carbon composite materials has become one of the key technological routes to overcome the inherent volume expansion bottleneck of silicon anodes and realize their commercial application. Currently, the raw materials for the preparation of porous carbon mainly include resins, coal, petroleum coke, and biomass. Among these, biomass, due to its wide availability, renewability, low cost, and environmental friendliness, has become one of the ideal raw materials for the preparation of porous carbon.

[0003] However, existing porous carbon materials prepared using biomass as a precursor have low specific surface areas and insufficient pore structure matching. For example, existing porous carbon materials prepared using biomass are mainly micropores, and their pore structure is poorly compatible with silane molecules, which is not conducive to the diffusion and deposition of silane molecules, resulting in a low silane loading and consequently poor electrochemical performance of the porous carbon material.

[0004] Therefore, how to provide an ideal porous carbon framework suitable for high-performance silicon-carbon anode materials, namely biomass-based porous carbon materials with high specific surface area, suitable pore structure and good surface chemical properties, is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] The purpose of this application is to provide a biomass-based porous carbon and its preparation method, and a silicon-carbon anode material and its preparation method, in order to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solution: A method for preparing biomass-based porous carbon, comprising: Biomass raw materials are mixed with urea to obtain pretreated materials; The pretreated material is mixed with the fermentation agent and then subjected to stacking aerobic fermentation. The fermentation product obtained from fermentation is dried to obtain a pre-porous precursor. The pre-porous precursor is carbonized in an inert atmosphere to obtain a carbonized product. An activation gas is introduced into the carbonization product to perform activation treatment, thereby obtaining biomass-based porous carbon.

[0007] According to embodiments of this application, the biomass raw materials include at least one of rice husks, corn stalks, sorghum stalks, and bamboo shavings; And / or, the moisture content w in the biomass raw material is 50-65%.

[0008] According to an embodiment of this application, the mixing of biomass feedstock and urea is carried out in a closed container; And / or, the temperature at which the biomass feedstock is mixed with urea is 20-30°C, and the mixing time of the biomass feedstock with urea is 2-12 hours; And / or, the mass of the urea accounts for 0.5-20% of the dry weight of the biomass, and the dry weight of the biomass is equal to the mass of the biomass feedstock multiplied by (1-w).

[0009] According to embodiments of this application, the fermenting agent is a natural compound fermentation agent; And / or, the fermentation agent accounts for 0.5-6% of the dry weight of the biomass; And / or, when carrying out aerobic fermentation in a stack, the method further includes: maintaining the temperature at the center of the stack at 20-70°C; And / or, the aerobic fermentation time of the stack is 2-15 days; And / or, the fermentation product is dried at a temperature of 80-110°C.

[0010] According to embodiments of this application, the inert atmosphere includes at least one of argon and nitrogen; And / or, the heating rate of the carbonization treatment is 2-20℃ / min; And / or, the carbonization treatment temperature is 400-600℃, and the carbonization treatment time is 1-6 hours; And / or, after the carbonization treatment is completed, the method further includes: cooling the material obtained from the carbonization treatment to room temperature, and then mechanically ball-milling it to a size that can pass through a 300-mesh sieve to obtain the carbonized product.

[0011] According to embodiments of this application, the activating gas includes water vapor or CO2; And / or, the flow rate of the activating gas is 50-150 mL / min; And / or, the heating rate of the activation treatment is 2-20℃ / min; And / or, the activation treatment temperature is 700-900℃, and the activation treatment time is 0.5-3 hours; And / or, after the activation treatment is completed, the method further includes: washing the activated product with water until neutral, and then drying it to obtain biomass-based porous carbon.

[0012] This application also provides a biomass-based porous carbon, which is prepared by the preparation method described above; And / or, the specific surface area of ​​the biomass-based porous carbon is 1602~1948 m². 2 ·g -1 The total pore volume of the biomass-based porous carbon is 1.51~1.72 cm³. 3 ·g -1 The mesopore volume of the biomass-based porous carbon is 0.85~1.05 cm³. 3 ·g -1 The micropore volume of the biomass-based porous carbon is 0.60~0.71 cm³. 3 ·g -1 .

[0013] This application also provides a method for preparing a silicon-carbon anode material, including: The biomass-based porous carbon described above is placed in a CVD furnace, and a mixture of silicon source and inert gas is introduced to perform silicon deposition, thereby obtaining silicon deposition products. A carbon source gas is introduced to perform carbon deposition, forming a carbon coating layer on the surface of the silicon deposition product, thus obtaining a silicon-carbon anode material. According to embodiments of this application, the inert gas includes Ar, the silicon source includes SiH4, and the carbon source includes acetylene; And / or, the volume fraction of the silicon source in the mixed gas is 2-10%; And / or, the flow rate of the mixed gas is 50-200 mL / min; And / or, the silicon deposition temperature is 450-650°C, and the silicon deposition time is 20-120 min; And / or, the flow rate of the carbon source gas is 50-120 mL / min; And / or, the carbon deposition temperature is 550-750℃, and the carbon deposition time is 30-120 min.

[0014] This application also provides a silicon-carbon anode material, which is prepared by the preparation method described above.

[0015] Compared with the prior art, the beneficial effects of this application include: This application combines fermentation and activation processes to synergistically regulate the pore structure of porous carbon materials. The biomass-based porous carbon prepared by this method possesses high specific surface area, a pore structure suitable for silane deposition, and excellent surface chemistry. Silicon-carbon anode materials prepared from this material exhibit superior electrochemical performance. Furthermore, the method for preparing biomass-based porous carbon in this application also has the advantages of being green, environmentally friendly, and having low production costs.

[0016] Specifically, in this application's method, urea is added before fermenting the biomass raw material. The biomass raw material is agricultural waste, a typical high-carbon, low-nitrogen material. Urea can supplement the nitrogen source required for microbial activity during fermentation, thereby promoting fermentation. Fermentation treatment can form a preliminary porous structure within the biomass raw material. Further activation treatment involves etching based on this preliminary porous structure to form a porous carbon material with a high specific surface area and suitable pore structure. This structure is suitable as a framework for silane deposition using CVD, which helps increase the silane loading and effectively buffers the volume expansion of silicon during charge and discharge, improving the electrochemical performance of the silicon-carbon anode material. Secondly, after urea decomposes, it undergoes an amination reaction with the biomass components, introducing nitrogen-containing groups. Through pyrolysis, nitrogen is anchored in the carbon framework, forming a stable nitrogen-doped carbon framework. This stable nitrogen-doped carbon framework promotes uniform silicon nucleation during silane deposition, improving the structural stability and electrochemical performance of the silicon-carbon anode material. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0018] Figure 1 This is a flowchart of the preparation method of biomass-based porous carbon in this application; Figure 2 The graph shows the cycling performance of Application Example 1 at a 0.5C rate. Detailed Implementation

[0019] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0020] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0021] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0022] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0023] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0024] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0025] A method for preparing biomass-based porous carbon, referenced Figure 1 ,include: Biomass raw materials are mixed with urea to obtain pretreated materials; The pretreated material is mixed with the fermentation agent and then subjected to stacking aerobic fermentation. The fermentation product obtained from fermentation is dried to obtain a pre-porous precursor. The pre-porous precursor is carbonized in an inert atmosphere to obtain a carbonized product. An activation gas is introduced into the carbonization product to perform activation treatment, thereby obtaining biomass-based porous carbon.

[0026] According to embodiments of this application, the biomass raw materials include at least one of rice husks, corn stalks, sorghum stalks, and bamboo shavings; these biomass raw materials are common agricultural or forestry processing by-products, and have the advantages of being inexpensive and readily available, which can effectively reduce production costs.

[0027] In some embodiments, the ash content of the biomass feedstock is 5 wt% or less, preferably 3 wt% or less. Using biomass feedstock with a lower ash content is beneficial for improving the purity of the final porous carbon material.

[0028] The moisture content w in the biomass raw material is 50-65%. If the moisture content in the biomass raw material is too low, microbial activity will not be able to proceed effectively; if the moisture content in the biomass raw material is too high, the material aeration will be poor, which will easily lead to anaerobic fermentation. The decomposition ability of microorganisms during anaerobic fermentation is weak, resulting in fewer pores in the porous carbon, which in turn makes it difficult to obtain silicon-carbon materials with excellent electrochemical performance after the prepared porous carbon silane is deposited.

[0029] In some embodiments, the moisture content w in the biomass feedstock is any value between 50%, 53%, 55%, 58%, 60%, 63%, 65%, or 50-65%.

[0030] According to an embodiment of this application, the mixing of biomass feedstock and urea is carried out in a closed container; In some embodiments, the temperature at which the biomass feedstock and urea are mixed is 20-30°C (e.g., 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, or any value between 20-30°C), and the mixing time between the biomass feedstock and urea is 2-12 hours (e.g., 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or any value between 2-12 hours). In some embodiments, the mass of the urea accounts for 0.5-20% of the dry weight of the biomass, and the dry weight of the biomass is equal to the mass of the biomass feedstock multiplied by (1-w).

[0031] For example, the mass of urea accounts for 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any value between 0.5% and 20% of the dry weight of biomass.

[0032] The urea introduced in this application can supplement the nitrogen source required for the metabolism of fermenting microorganisms, promoting their growth and reproduction, and facilitating the degradation of biomass raw materials to form porous structures. Furthermore, the nitrogen introduced into the urea reacts chemically with the carbon skeleton, achieving in-situ doping of nitrogen into the carbon skeleton and forming stable nitrogen doping in the final porous carbon material. Nitrogen doping not only improves the conductivity of porous carbon but also acts as an active site during subsequent chemical vapor deposition of silicon, promoting uniform silicon nucleation and thus comprehensively improving the electrochemical performance of the silicon-carbon anode material. Insufficient urea addition will result in low fermentation efficiency and insufficient nitrogen doping, affecting the electrochemical performance of the silicon-carbon anode material. Excessive urea addition will cause nitrogen loss and significant pH fluctuations due to ammonia volatilization, inhibiting beneficial microbial activity and potentially leaving excessive unstable nitrogen-containing substances in the final carbon material. These unstable nitrogen-containing substances will become active sites for electrolyte decomposition during subsequent battery charging and discharging, exacerbating irreversible side reactions.

[0033] According to embodiments of this application, the fermenting agent is a natural compound fermentation agent; In some embodiments, the natural compound fermentation agent is the Jinbaobei substrate nutrient soil fermentation agent; During fermentation, enzymes secreted by microorganisms selectively degrade lignocellulose in biomass, etching natural pores into the biomass matrix. Fermentation builds a rich initial pore network before activation, providing more reaction sites and diffusion channels for subsequent steam activation. This pore-forming technology is green and environmentally friendly, with mild fermentation conditions, no need for highly corrosive chemical reagents, simple post-processing, and is environmentally friendly.

[0034] In some embodiments, the fermentation agent accounts for 0.5-6% of the dry biomass mass. When the amount of fermentation agent added is within the above range, sufficient effective microbial communities can be inoculated to maintain the stable progress of the fermentation process. If the amount of fermentation agent added is too small, the fermentation cycle will be prolonged or the fermentation will be insufficient. If the amount of fermentation agent added is too large, the reaction may be too violent, which may form some macropores. This will result in a relative lack of micropores that can support silicon active materials and provide reaction sites, which will lead to a low silicon loading in the prepared silicon-carbon anode material and affect the electrochemical performance of the silicon-carbon anode material.

[0035] For example, the mass of the starter culture can be any value between 0.5%, 1%, 2%, 3%, 4%, 5%, 6% or 0.5-6% of the dry mass of the biomass.

[0036] In some embodiments, when performing aerobic fermentation in a stack, the method further includes maintaining the temperature at the center of the stack at 20-70°C; for example, the temperature at the center of the stack is any value between 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 20-70°C.

[0037] In some embodiments, during the fermentation process, the method further includes: real-time monitoring and dynamic adjustment of the temperature at the center of the pile to maintain the temperature at the center of the pile at 20-70°C.

[0038] Specifically, during fermentation, when the temperature at the center of the pile reaches 50-70℃, the pile is first turned over to ensure even distribution of temperature and oxygen. Subsequently, the temperature is continuously adjusted based on monitoring. When the temperature at the center of the pile reaches 60℃ again, the pile is turned over once more to maintain the material temperature within the 50-70℃ range throughout the fermentation process, while simultaneously maintaining good aerobic conditions to ensure efficient and stable fermentation.

[0039] In some embodiments, the aerobic fermentation time of the stack is 2-15 days; for example, the aerobic fermentation time of the stack is any value between 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 14 days, 15 days, or 2-15 days.

[0040] In some embodiments, the fermentation product is dried at a temperature of 80-110°C (e.g., 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, or any value between 80-110°C). Drying removes moisture, yielding a pre-porous precursor.

[0041] According to embodiments of this application, the inert atmosphere includes at least one of argon and nitrogen; In some embodiments, the heating rate of the carbonization process is 2-20℃ / min; for example, the heating rate of the carbonization process is 2℃ / min, 5℃ / min, 7℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, 17℃ / min, 20℃ / min or any value between 2-20℃ / min.

[0042] In some embodiments, the carbonization temperature is 400-600°C, and the carbonization time is 1-6 hours; for example, the carbonization temperature is 400°C, 420°C, 450°C, 470°C, 500°C, 520°C, 550°C, 570°C, 600°C, or any value between 400-600°C; the carbonization time is 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any value between 1-6 hours.

[0043] In some embodiments, after the carbonization treatment is completed, the method further includes: cooling the material obtained by the carbonization treatment to room temperature, and then mechanically ball-milling it to pulverize it to pass through a 300-mesh sieve to obtain the carbonization product; Furthermore, the grinding media of the mechanical ball mill is zirconia balls, the container of the mechanical ball mill is a zirconia jar, the ball-to-material ratio of the mechanical ball mill is 10-30:1, the ball milling speed is 300-800 r / min, and the ball milling time is 1-4 hours.

[0044] According to embodiments of this application, the activating gas includes water vapor or CO2; In some embodiments, the flow rate of the activating gas is 50-150 mL / min; for example, the flow rate of the activating gas is 50 mL / min, 70 mL / min, 100 mL / min, 120 mL / min, 150 mL / min or any value between 50-150 mL / min.

[0045] In some embodiments, the heating rate of the activation treatment is 2-20℃ / min; for example, the heating rate of the activation treatment is 2℃ / min, 5℃ / min, 7℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, 17℃ / min, 20℃ / min or any value between 2-20℃ / min.

[0046] In some embodiments, the activation treatment temperature is 700-900°C, and the activation treatment time is 0.5-3 hours; for example, the activation treatment temperature is 700°C, 720°C, 750°C, 770°C, 800°C, 820°C, 850°C, 870°C, 900°C, or any value between 700-900°C; the activation treatment time is 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or any value between 0.5-3 hours.

[0047] Based on the pre-pore formation during fermentation, the carbon skeleton can be further etched through activation treatment to generate abundant pores.

[0048] In some embodiments, after the activation treatment is completed, the method further includes: washing the activated product with water until neutral, and then drying it to obtain biomass-based porous carbon.

[0049] This application also provides a biomass-based porous carbon, which is prepared by the preparation method described above.

[0050] In some embodiments, the specific surface area of ​​the biomass-based porous carbon is 1602~1948 m². 2 ·g-1 For example, the specific surface area of ​​biomass-based porous carbon is 1602 m². 2 ·g -1 1650 m 2 ·g -1 1700 m 2 ·g -1 1750 m 2 ·g -1 1800m 2 ·g -1 1850 m 2 ·g -1 1900 m 2 ·g -1 1948 m 2 ·g -1 Or 1602~1948 m 2 ·g -1 Any value between.

[0051] In some embodiments, the total pore volume of the biomass-based porous carbon is 1.51~1.72 cm³. 3 ·g -1 For example, the total pore volume of biomass-based porous carbon is 1.51 cm³. 3 ·g -1 1.6 cm 3 ·g -1 1.65 cm 3 ·g -1 1.7 cm 3 ·g -1 1.72cm 3 ·g -1 Or 1.51~1.72cm 3 ·g -1 Any value between.

[0052] In some embodiments, the mesopore volume of the biomass-based porous carbon is 0.85~1.05 cm³. 3 ·g -1 For example, the mesopore volume of biomass-based porous carbon is 0.85 cm³. 3 ·g -1 0.9 cm 3 ·g -1 0.95 cm 3 ·g -1 1 cm 3 ·g -1 1.05 cm 3 ·g -1 Or 0.85~1.05cm 3 ·g -1Any value between.

[0053] In some embodiments, the micropore volume of the biomass-based porous carbon is 0.60~0.71 cm³. 3 ·g -1 For example, the micropore volume of biomass-based porous carbon is 0.60 cm³. 3 ·g -1 0.65 cm 3 ·g -1 0.7 cm 3 ·g -1 0.71 cm 3 ·g -1 Or 0.60~0.71cm 3 ·g -1 Any value between.

[0054] This application also provides a method for preparing a silicon-carbon anode material, including: The biomass-based porous carbon described above is placed in a CVD furnace, and a mixture of silicon source and inert gas is introduced to perform silicon deposition, thereby obtaining silicon deposition products. A carbon source gas is introduced to perform carbon deposition, forming a carbon coating layer on the surface of the silicon deposition product, thus obtaining a silicon-carbon anode material. According to embodiments of this application, the inert gas includes Ar, the silicon source includes SiH4, and the carbon source includes acetylene; In some embodiments, the volume fraction of the silicon source in the mixed gas is 2-10%; for example, the volume fraction of the silicon source in the mixed gas is any value between 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or 2-10%.

[0055] In some embodiments, the gas flow rate of the mixed gas is 50-200 mL / min; for example, the gas flow rate of the mixed gas is 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 140 mL / min, 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min, 190 mL / min, 200 mL / min or any value between 50-200 mL / min.

[0056] In some embodiments, the silicon deposition temperature is 450-650°C, and the silicon deposition time is 20-120 min; for example, the silicon deposition temperature is any value between 450°C, 500°C, 550°C, 600°C, 650°C, or 450-650°C, and the silicon deposition time is any value between 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or 20-120 min.

[0057] In some embodiments, the flow rate of the carbon source gas is 50-120 mL / min; for example, the flow rate of the carbon source gas is 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, 110 mL / min, 120 mL / min or any value between 50-120 mL / min; In some embodiments, the carbon deposition temperature is 550-750°C, and the carbon deposition time is 30-120 min. For example, the carbon deposition temperature is 550°C, 600°C, 650°C, 700°C, 750°C, or any value between 550-750°C, and the carbon deposition time is 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or any value between 30-120 min.

[0058] This application also provides a silicon-carbon anode material, which is prepared by the preparation method described above.

[0059] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0060] The fermentation agent used in the following examples and comparative examples was purchased from Beijing Huaxia Kangyuan Technology Co., Ltd., product name: Jinbaobei substrate nutrient soil fermentation agent.

[0061] Example 1 Example 1 provides a biomass-based porous carbon, the preparation method of which includes: (1) Preparation of biomass raw materials: The rice husks were crushed and sieved through a 50-mesh sieve, and then washed to remove impurities. They were then dried at 80°C until the moisture content was 58%, resulting in rice husk powder with a moisture content of 58% and an ash content of 2wt%. (2) Preparation of pretreated material: Take 100g of rice husk powder with a moisture content of 58% obtained in step (1) and mix it with 4.2g of urea (the mass of urea accounts for 10% of the dry basis mass of rice husk powder). Place it in a closed tank and let it stand for 6 hours to obtain pretreated material. (3) Fermentation treatment: Add 0.84g of Jinbaobei fermentation agent (the mass of the fermentation agent accounts for 2% of the dry mass of rice husk powder) to the pretreated material and mix it. After the mixture is finished, it is piled up. When the temperature of the mixture reaches 60℃, it is turned over once and fermented for 8 days (from the start of fermentation after adding the fermentation agent to the end of fermentation).

[0062] (4) Drying treatment: After fermentation, the product is placed in a 100℃ oven for drying to remove moisture and obtain the pre-porous precursor.

[0063] (5) Carbonization treatment: The pre-pore precursor is placed in a tube furnace and carbonized at 500℃ for 4 hours under argon atmosphere at a rate of 5℃ / min. After cooling, it is taken out and mechanically ball-milled at a ball-to-material ratio of 10:1 and a rotation speed of 400r / min. After ball milling for 2 hours, it is sieved through a 300-mesh sieve to obtain the carbonized product.

[0064] (6) Activation treatment: The carbonized product is placed in a tube furnace. First, argon gas is introduced into the furnace for 1 hour to purge the air. After 1 hour, heating is started. The temperature is increased to 850°C at 5°C / min. Water vapor is introduced at a flow rate of 80 mL / min to activate for 2 hours. After the activation is completed, the water vapor is turned off and argon gas is introduced. The temperature drops to room temperature under argon protection to obtain the activated porous carbon material.

[0065] (7) Post-treatment: The activated porous carbon material was centrifuged and washed with deionized water until neutral, and dried overnight at 80°C to obtain biomass-based porous carbon.

[0066] Example 2 The difference between Example 2 and Example 1 is that the amount of urea added in step (2) is changed to 2.1g (the mass of urea accounts for 5% of the dry weight of rice husk powder). Everything else is the same as in Example 1.

[0067] Example 3 The difference between Example 3 and Example 1 is that the amount of urea added in step (2) is changed to 6.3g (the mass of urea accounts for 15% of the dry weight of rice husk powder). Everything else is the same as in Example 1.

[0068] Example 4 The difference between Example 4 and Example 1 is that the amount of fermenting agent added in step (3) is changed to 0.42g (the mass of the fermenting agent accounts for 1% of the dry weight of the rice husk powder). Everything else is the same as in Example 1.

[0069] Example 5 The difference between Example 5 and Example 1 is that the amount of fermenting agent added in step (3) is changed to 1.68g (the mass of the fermenting agent accounts for 4% of the dry weight of the rice husk powder). Everything else is the same as in Example 1.

[0070] Example 6 The difference between Example 6 and Example 1 is that the fermentation time in step (3) is changed to 12 days. Everything else is the same as in Example 1.

[0071] Example 7 The difference between Example 7 and Example 1 is that the fermentation time in step (3) is changed to 5 days. Everything else is the same as in Example 1.

[0072] Example 8 The difference between Example 8 and Example 1 is that the rice husks in Example 1 are replaced with corn stalks. Everything else is the same as in Example 1.

[0073] Example 9 The difference between Example 9 and Example 1 is that the rice husks in Example 1 are replaced with sorghum straw. Everything else is the same as in Example 1.

[0074] Example 10 The difference between Example 10 and Example 1 is that the rice husks in Example 1 are replaced with bamboo shavings. Everything else is the same as in Example 1.

[0075] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that steps (2) and (3) are omitted, that is, urea and fermentation agent are not added, and the product of step (1) is directly processed in step (4). Everything else is the same as in Example 1.

[0076] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that step (2) is omitted, and the product of step (1) is directly subjected to fermentation treatment in step (3). Everything else is the same as in Example 1.

[0077] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that step (3) of fermentation is omitted, and the product of step (2) is directly processed in step (4). Everything else is the same as in Example 1.

[0078] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that: the fermentation treatment in steps (2) and (3) and the activation treatment in step (6) are omitted, and the product of step (1) is directly processed in step (4). After the treatment in step (4), step (5) is carried out, and the product of step (5) is directly processed in step (7). Everything else is the same as in Example 1.

[0079] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that urea in step (2) is replaced with ammonium nitrate. In Example 1, the amount of urea added was 4.2g, and its nitrogen content was 46.7%. The mass of nitrogen element added in Example 1 was 1.96g. In Comparative Example 5, the amount of nitrogen element added was the same as in Example 1, and the nitrogen content of ammonium nitrate was 34%. The amount of ammonium nitrate added was 5.76g. The remaining steps were the same as in Example 1.

[0080] The nitrogen content of the biomass-based porous carbon in the examples and comparative examples was determined by nitrogen adsorption-desorption tests and elemental analysis. The test data are shown in the table below: Table 1. Adsorption-desorption data and nitrogen content of porous carbon materials in each embodiment and comparative example.

[0081] As can be seen from Table 1, the specific surface area, total pore volume, mesopore volume, and micropore volume of the porous carbon materials in Examples 1-10 are all higher than those in Comparative Examples 1-5, which is more conducive to silane vapor deposition and improves the electrochemical performance of silicon-carbon anode materials.

[0082] Comparative Example 5 uses ammonium nitrate as a nitrogen source. Its decomposition behavior is different from that of urea, making it difficult to form a stable nitrogen-doped structure, resulting in a low nitrogen content in the prepared porous carbon material.

[0083] Application Example 1-10 and Comparative Application Example 1-5 The porous carbon materials prepared in Examples 1-10 and Comparative Examples 1-5 were placed in a CVD furnace. Under an Ar atmosphere, the gas flow rate was 100 mL / min, and the temperature was increased to 500°C at a heating rate of 5°C / min. Then, a SiH4 / Ar mixed gas (SiH4 accounted for 5% of the volume in the mixed gas) was introduced at a gas flow rate of 100 mL / min for silane deposition for 30 min. After deposition, the silane mixed gas was turned off. At 650°C, acetylene gas was introduced at a gas flow rate of 60 mL / min for carbon source deposition for 60 min. After deposition, the acetylene gas was turned off, and the materials were cooled to room temperature under an Ar protective gas to obtain the silicon-carbon materials of Application Examples 1-10 and Comparative Application Examples 1-5.

[0084] Batteries were prepared using silicon-carbon anode materials from Application Examples 1-10 and Comparative Application Examples 1-5 under the same conditions. Specifically, the following steps were taken: silicon-carbon anode material, conductive agent, styrene-butadiene rubber, and sodium carboxymethyl cellulose were added to a homogenizing tank at a mass ratio of 90:4:3:3, with deionized water as the solvent. The mixture was homogenized using a degassing machine, coated onto copper foil, and then dried overnight at 80°C in a vacuum oven. The dried electrode sheets were cut into round pieces and transferred to an argon glove box for button cell assembly. The counter electrode for button cell assembly was a lithium metal sheet, and the electrolyte formulation was: 1 mol / L LiPF6 dissolved in a 1:1 volume ratio of EC and DMC mixed solvent, with 5% FEC added. Finally, the cells were encapsulated in a coin cell casing and allowed to stand for at least 12 hours. Electrochemical performance tests were conducted under the same conditions, including initial coulombic efficiency and cycle performance (100 cycles at 0.5C). The test results are shown in the table below.

[0085] Table 2 Electrochemical performance data for each application example and comparative application example

[0086] From Table 2 and Figure 2 It can be seen that the silicon-carbon anode material in Application Examples 1-10 has both high initial coulombic efficiency and high cycle stability, and its electrochemical performance is significantly better than that of Comparative Application Examples 1-5.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0088] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing biomass-based porous carbon, characterized in that, include: Biomass raw materials are mixed with urea to obtain pretreated materials; The pretreated material is mixed with the fermentation agent and then subjected to stacking aerobic fermentation. The fermentation product obtained from fermentation is dried to obtain a pre-porous precursor. The pre-porous precursor is carbonized in an inert atmosphere to obtain a carbonized product. An activation gas is introduced into the carbonization product to perform activation treatment, thereby obtaining biomass-based porous carbon.

2. The method for preparing biomass-based porous carbon according to claim 1, characterized in that, The biomass raw materials include at least one of rice husks, corn stalks, sorghum stalks, and bamboo shavings; And / or, the moisture content w in the biomass raw material is 50-65%.

3. The method for preparing biomass-based porous carbon according to claim 2, characterized in that, The mixing of biomass feedstock and urea is carried out in a closed container; And / or, the temperature at which the biomass feedstock is mixed with urea is 20-30°C, and the mixing time of the biomass feedstock with urea is 2-12 hours; And / or, the mass of the urea accounts for 0.5-20% of the dry weight of the biomass, and the dry weight of the biomass is equal to the mass of the biomass feedstock multiplied by (1-w).

4. The method for preparing biomass-based porous carbon according to claim 1, characterized in that, The fermentation agent is a natural compound fermentation agent; And / or, the fermentation agent accounts for 0.5-6% of the dry weight of the biomass; And / or, when carrying out aerobic fermentation in a stack, the method further includes: maintaining the temperature at the center of the stack at 20-70°C; And / or, the aerobic fermentation time of the stack is 2-15 days; And / or, the fermentation product is dried at a temperature of 80-110°C.

5. The method for preparing biomass-based porous carbon according to claim 1, characterized in that, The inert atmosphere includes at least one of argon and nitrogen; And / or, the heating rate of the carbonization treatment is 2-20℃ / min; And / or, the carbonization treatment temperature is 400-600℃, and the carbonization treatment time is 1-6 hours; And / or, after the carbonization treatment is completed, the method further includes: cooling the material obtained from the carbonization treatment to room temperature, and then mechanically ball-milling it to a size that can pass through a 300-mesh sieve to obtain the carbonized product.

6. The method for preparing biomass-based porous carbon according to any one of claims 1-5, characterized in that, The activating gas includes water vapor or CO2; And / or, the flow rate of the activating gas is 50-150 mL / min; And / or, the heating rate of the activation treatment is 2-20℃ / min; And / or, the activation treatment temperature is 700-900℃, and the activation treatment time is 0.5-3 hours; And / or, after the activation treatment is completed, the method further includes: washing the activated product with water until neutral, and then drying it to obtain biomass-based porous carbon.

7. A biomass-based porous carbon, characterized in that, The biomass-based porous carbon is prepared by the preparation method according to any one of claims 1-6; And / or, the specific surface area of ​​the biomass-based porous carbon is 1602~1948 m². 2 ·g -1 The total pore volume of the biomass-based porous carbon is 1.51~1.72 cm³. 3 ·g -1 The mesopore volume of the biomass-based porous carbon is 0.85~1.05 cm³. 3 ·g -1 The micropore volume of the biomass-based porous carbon is 0.60~0.71 cm³. 3 ·g -1 .

8. A method for preparing a silicon-carbon anode material, characterized in that, include: The biomass-based porous carbon described in claim 7 is placed in a CVD furnace, and a mixed gas of silicon source and inert gas is introduced to perform silicon deposition to obtain a silicon deposition product. A carbon source gas is introduced to perform carbon deposition, forming a carbon coating layer on the surface of the silicon deposition product, thus obtaining a silicon-carbon anode material.

9. The method for preparing the silicon-carbon anode material according to claim 8, characterized in that, The inert gas includes Ar, the silicon source includes SiH4, and the carbon source includes acetylene; And / or, the volume fraction of the silicon source in the mixed gas is 2-10%; And / or, the flow rate of the mixed gas is 50-200 mL / min; And / or, the silicon deposition temperature is 450-650°C, and the silicon deposition time is 20-120 min; And / or, the flow rate of the carbon source gas is 50-120 mL / min; And / or, the carbon deposition temperature is 550-750℃, and the carbon deposition time is 30-120 min.

10. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material is prepared by the preparation method described in claim 8 or 9.

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