Bamboo-based hard carbon material, preparation method thereof and sodium ion battery

Abstract

The invention belongs to the technical field of materials, and provides a bamboo-based hard carbon material and a preparation method thereof, and a sodium ion battery, during preparation, a bamboo-based material and a 2-4wt% alkali solution are mixed according to a mass ratio of 1: 5, boiling is performed for 1-2 hours, cooling is performed, and then filter pressing separation is performed. And filtering, sealing the filtrate for later use, washing filter residues to be neutral, drying, pre-carbonizing, crushing by a jet mill, pickling, washing, drying to obtain a pickled material, carbonizing at high temperature, and cooling to obtain the bamboo-based hard carbon material. The process has the remarkable advantages that part of lignin is removed through soda boiling, excessive graphitization of hard carbon is inhibited, the carbon layer spacing is increased, the carbon domain size is shortened, more closed pores are formed, and the reversible capacity and the ion transport dynamics performance are improved; the soda boiling filtrate is rich in lignin and a small amount of polysaccharide and hemicellulose, can form a long-range large-interlayer-spacing graphite domain when being used for subsequent coating, induces to form a high-quality SEI film and assists ion conduction, greatly improves the first coulombic efficiency and the dynamic performance, comprehensively optimizes the electrochemical performance, and builds a foundation for commercial application of the soda boiling filtrate in sodium battery negative electrodes.

Description

Technical Field

[0001] This application belongs to the field of materials technology, and in particular relates to a bamboo-based hard carbon material and its preparation method, and a sodium-ion battery. Background Technology

[0002] The development of green energy storage materials with low cost, high performance, and sustainability as core objectives has become a focus of the industry. Hard carbon materials, with their disordered microcrystalline structure, abundant defects, and large interlayer spacing, have shown superior potential compared to traditional graphite in sodium-ion battery anode applications, making them a key candidate material for next-generation large-scale energy storage systems. However, their precursors have significant limitations: fossil-based precursors (such as pitch and phenolic resin) are non-renewable, costly, and pollute a lot during preparation; while biomass-based precursors (such as coconut shells, starch, and lignin) are renewable, they face performance bottlenecks such as poor structural uniformity, difficulty in microstructure control, and difficulty in balancing reversible capacity and first-efficiency performance, which restricts their commercial application.

[0003] Bamboo is an ideal candidate for hard carbon precursors due to its rapid growth and high renewability. It has unique advantages such as a natural multi-level pore structure (from macroscopic pores of vascular bundles to microscopic nanopores of cell walls, forming a continuous transport network), its own inorganic components (such as potassium silicate, which can help form nanopores), and high carbon content and high strength (high carbonization yield and stable mechanical structure of carbides). These advantages provide a good foundation for the preparation of high-performance carbon materials and can theoretically overcome some of the limitations of existing precursors.

[0004] However, the preparation of high-performance hard carbon from bamboo by direct carbonization still faces significant technical bottlenecks: high-temperature carbonization can easily lead to the collapse of the natural fine structure of bamboo and pore blockage, resulting in an uncontrolled increase in specific surface area, exacerbating side reactions and reducing the first-cycle coulombic efficiency (ICE); if inorganic elements such as silicon and potassium in bamboo are not properly treated, they will remain as ash, affecting the electrical conductivity of carbon materials and impairing cycling stability; existing pretreatment processes are crude and cannot achieve synergistic regulation of the chemical composition and microstructure of bamboo, and the "structure-performance" relationship is vague, making it difficult to retain the advantages of bamboo and optimize sodium storage sites and control surface chemical properties through process design. These problems have not yet been systematically solved. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing bamboo-based hard carbon materials, which aims to solve the problems in the prior art where direct carbonization using bamboo as a hard carbon precursor easily leads to the collapse of the natural structure and the residue of impurities, and the crude pretreatment process makes it difficult to achieve synergistic regulation of the chemical composition and microstructure of bamboo.

[0006] The embodiments of this application are implemented as follows: a method for preparing bamboo-based hard carbon material includes: Bamboo-based material is mixed with 2-4 wt% alkaline solution at a mass ratio of 1:5, boiled for 1-2 hours, and then naturally cooled to room temperature. Solid-liquid separation is achieved by pressure filtration. The resulting filtrate is sealed and stored for later use. The filter residue is washed with deionized water until neutral, dried, and then stored for later use. The dried filter residue is pre-carbonized, and the pre-carbonized product is crushed by an air jet mill and then pickled. The pickled product is filtered, washed with deionized water until neutral, and dried to obtain the pickled material. The pickled material is subjected to high-temperature carbonization treatment and then cooled to obtain bamboo-based hard carbon material.

[0007] Another objective of this application is to provide a bamboo-based hard carbon material, which is prepared by the above-described method for preparing bamboo-based hard carbon materials.

[0008] Another objective of this application is to provide a sodium-ion battery comprising the aforementioned bamboo-based hard carbon material.

[0009] This application provides a method for preparing bamboo-based hard carbon materials, which has significant advantages over existing technologies. On the one hand, by removing some lignin from bamboo shavings through alkaline boiling, excessive graphitization of the hard carbon material can be effectively inhibited. This not only increases the carbon interlayer spacing and shortens the carbon domain size, but also promotes the formation of more closed-pore structures, thereby significantly improving the reversible capacity and ion transport kinetics of the hard carbon material. On the other hand, the filtrate produced by alkaline boiling is rich in lignin and contains a small amount of polysaccharides and hemicellulose. When used for subsequent coating treatment, these substances can coordinate the formation of long-range graphite domains with large interlayer spacing. This structure can induce the formation of a thin and robust solid electrolyte interphase (SEI) film during battery charging and discharging, while also facilitating efficient ion conduction. Ultimately, this results in higher first coulombic efficiency (ICE) and better kinetic performance of the bamboo-based hard carbon material, comprehensively improving the electrochemical performance of the material and laying the foundation for its commercial application in sodium-ion battery anodes. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0011] This application provides a method for preparing bamboo-based hard carbon material, including: Bamboo-based material is mixed with 2-4 wt% alkaline solution at a mass ratio of 1:5, boiled for 1-2 hours, and then naturally cooled to room temperature. Solid-liquid separation is achieved by pressure filtration. The resulting filtrate is sealed and stored for later use. The filter residue is washed with deionized water until neutral, dried, and then stored for later use. The dried filter residue is pre-carbonized, and the pre-carbonized product is crushed by an air jet mill and then pickled. The pickled product is filtered, washed with deionized water until neutral, and dried to obtain the pickled material. The pickled material is subjected to high-temperature carbonization treatment and then cooled to obtain bamboo-based hard carbon material.

[0012] In a preferred embodiment of this application, the pickled material is subjected to high-temperature carbonization treatment, and after cooling, a bamboo-based hard carbon material is obtained, comprising: The pickled material and the stored filtrate were stirred and mixed at a mass ratio of 1:10-20. The pH value of the mixture was adjusted to 5-7 so that the lignin in the filtrate precipitated and uniformly coated on the surface of the bamboo charcoal. Then, the solid and liquid were separated by pressure filtration. The resulting filter cake was washed and dried to obtain the coated material. The coated material is subjected to high-temperature carbonization treatment, and after cooling, bamboo-based hard carbon material is obtained.

[0013] In a preferred embodiment of this application, the pre-carbonization conditions are as follows: pre-carbonization temperature is 400-600℃, heating rate is 5℃ / min, pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0014] In a preferred embodiment of this application, air jet milling is used to control the particle size D50 to be 5±0.5μm.

[0015] In a preferred embodiment of this application, the pickling conditions are as follows: the pickling solution is a 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the pickling temperature is 80°C, and the pickling time is 12 h.

[0016] In a preferred embodiment of this application, the pH value is adjusted to 5-7 using one or more of carbon dioxide, hydrochloric acid, acetic acid, citric acid, sulfuric acid, nitric acid, and oxalic acid.

[0017] In a preferred embodiment of this application, the high-temperature carbonization conditions are: carbonization temperature of 1100-1300℃, carbonization time of 3h, heating rate of 2℃ / min, and under N2 / Ar atmosphere.

[0018] In a preferred embodiment of this application, the alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.

[0019] The following detailed description of bamboo-based hard carbon materials, their preparation methods, and sodium-ion batteries is provided through specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0020] Example 1: Preparation of bamboo-based hard carbon materials S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with a 4 wt% NaOH solution at a mass ratio of 1:5, and then boil for 2 hours.

[0021] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0022] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0023] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0024] S5. The pre-carbonized material crushed in step S4 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0025] S6. Mix the pickling material from step S5 with the filtrate from step S2 at a mass ratio of 1:10. Stir for 30 minutes, then introduce CO2 to adjust the pH to 5-7, causing lignin to precipitate and uniformly coat the surface of the bamboo charcoal. Stir for another 30 minutes (continuously introducing CO2 to maintain the weak acidity of the solution), then filter by pressure to separate the solid and liquid. Wash the filter cake 2-3 times with the same volume of deionized water as the filtrate, then dry it for later use to obtain the coated material.

[0026] S7. The coated material from step S6 is then subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0027] Example 2: Preparation of bamboo-based hard carbon materials S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with a 2 wt% NaOH solution at a mass ratio of 1:5, and then boil for 2 hours.

[0028] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0029] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0030] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0031] S5. The pre-carbonized material crushed in step S4 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0032] S6. Mix the pickling material from step S5 with the filtrate from step S2 at a mass ratio of 1:20. Stir for 30 minutes, then introduce CO2 to adjust the pH to 5-7, causing lignin to precipitate and uniformly coat the surface of the bamboo charcoal. Stir for another 30 minutes (continuously introducing CO2 to maintain the weak acidity of the solution), then filter by pressure to separate the solid and liquid. Wash the filter cake 2-3 times with the same volume of deionized water as the filtrate, then dry it for later use to obtain the coated material.

[0033] S7. The coated material from step S6 is subjected to high-temperature carbonization in a tube furnace at a temperature of 1300 ℃. The carbonization time is 3 h, the heating rate is 2 ℃ / min, and the atmosphere is N2.

[0034] Example 3: Preparation of bamboo-based hard carbon materials S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with a 4 wt% NaOH solution at a mass ratio of 1:5, and then boil for 2 hours.

[0035] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0036] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0037] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0038] S5. The pre-carbonized material crushed in step S4 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0039] S6. The pickled material from step S5 is subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0040] Example 4: Preparation of bamboo-based hard carbon materials S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with a 4 wt% NaOH solution at a mass ratio of 1:5, and then boil for 1 hour.

[0041] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0042] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0043] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0044] S5. The pre-carbonized material crushed in step S4 is acid-washed to obtain acid-washed material. The acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80 ℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral and dried at 105 ℃ to constant weight.

[0045] S6. Mix the pickling material from step S5 with the filtrate from step S2 at a mass ratio of 1:14. Stir for 30 minutes, then introduce CO2 to adjust the pH to 5-7, causing lignin to precipitate and uniformly coat the bamboo charcoal surface. Stir for another 30 minutes (continuously introducing CO2 to maintain the weak acidity of the solution), then filter by pressure to separate the solid and liquid. Wash the filter cake 2-3 times with the same volume of deionized water as the filtrate, then dry it for later use to obtain the coated material.

[0046] S7. The coated material from step S6 is then subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0047] Comparative Example 1: Preparation of bamboo-based hard carbon materials S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with a 6wt% NaOH solution at a mass ratio of 1:5, and then boil for 2 hours.

[0048] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0049] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0050] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0051] S5. The pre-carbonized material crushed in step S4 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0052] S6. The pickled material from step S5 is subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0053] Comparative Example 2: Preparation of bamboo-based hard carbon materials S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with deionized water at a mass ratio of 1:5, and then boil for 2 hours.

[0054] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0055] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0056] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0057] S5. The pre-carbonized material crushed in step S4 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0058] S6. The pickled material from step S5 is subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0059] Comparative Example 3: Preparation of bamboo-based hard carbon materials S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with a 4 wt% NaOH solution at a mass ratio of 1:5, and then boil for 3 hours.

[0060] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0061] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0062] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0063] S5. The pre-carbonized material crushed in step S4 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0064] S6. The pickled material from step S5 is subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0065] Comparative Example 4: Preparation of bamboo-based hard carbon materials S1. Collect and clean the waste bamboo shavings from the bamboo product factory for later use. Pre-carbonize the bamboo shavings in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0066] S2. The pre-carbonized material from step S1 is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0067] S3. The pre-carbonized material crushed in step S2 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0068] S4. The pickled material from step S4 above is subjected to high-temperature carbonization in a tube furnace at a carbonization temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0069] Comparative Example 5: Preparation of bamboo-based hard carbon materials S1. Collect and clean the bamboo shavings discarded from the bamboo product factory for later use. Pre-carbonize the bamboo shavings in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0070] S2. The pre-carbonized material from step S1 is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0071] S3. The pre-carbonized material crushed in step S2 above is acid-washed to obtain acid-washed material; the acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral, and dried at 105℃ to constant weight.

[0072] S4. Mix the above-mentioned pickled material with the filtrate from step S2 in Example 1 at a mass ratio of 1:10. After stirring for 30 minutes, introduce CO2 to adjust the pH value to 5-7, causing lignin to precipitate and uniformly coat the surface of the bamboo charcoal. Stir for another 30 minutes (continuously introducing CO2 to maintain the weak acidity of the solution), then filter by pressure to separate the solid and liquid. Wash the filter cake 2-3 times with the same volume of deionized water as the filtrate, then dry it for later use to obtain the coated material.

[0073] S5. The coated material from step S4 is then subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0074] Comparative Example 6 S1. Collect and wash the waste bamboo shavings from the bamboo product factory for later use. Mix the bamboo shavings with a 4 wt% NaOH solution at a mass ratio of 1:5, and then boil for 2 hours.

[0075] S2. After the above slurry has cooled naturally to room temperature, filter it by pressure to separate the solid and liquid. Store the filtrate in a sealed container for later use, and wash the filter residue with deionized water until neutral, then dry it for later use.

[0076] S3. The filter residue from step S2 above is pre-carbonized in a box furnace to obtain pre-carbonized material; the pre-carbonization temperature is 400℃, the heating rate is 5℃ / min, the pre-carbonization time is 2 h, and the atmosphere is N2 / Ar.

[0077] S4. The pre-carbonized material from step S3 above is crushed by an air jet mill to control the particle size D50 to be 5±0.5μm.

[0078] S5. The pre-carbonized material crushed in step S4 is acid-washed to obtain acid-washed material. The acid-washing solution is 1 M hydrochloric acid solution, the material-to-liquid ratio is 1:5, the acid-washing temperature is 80 ℃, and the acid-washing time is 12 h. After filtration, it is washed with deionized water until neutral and dried at 105 ℃ to constant weight.

[0079] S6. The filtrate from step S2 was purged with CO2 to adjust the pH to 5-7, causing lignin to precipitate. The filtrate was then dried to constant weight, and the lignin concentration in the filtrate was measured to be 36 g / L. Commercial lignin (Tianjin Damao Chemical Reagent Co., Ltd.) was dissolved in 4 wt% NaOH solution to prepare a lignin solution of the same concentration.

[0080] The pickled material from step S5 above is mixed with the lignin solution at a mass ratio of 1:10. After stirring for 30 minutes, CO2 is introduced to adjust the pH value to 5-7, causing the lignin to precipitate and uniformly coat the surface of the bamboo charcoal. After stirring for another 30 minutes (continuously introducing CO2 to maintain the weak acidity of the solution), the mixture is filtered to separate the solid and liquid. The filter cake is washed 2-3 times with the same volume of deionized water as the solution and then dried for later use, yielding the coated material.

[0081] S7. The coated material from step S6 is then subjected to high-temperature carbonization in a tube furnace at a temperature of 1300℃. The carbonization time is 3 hours, the heating rate is 2℃ / min, and the atmosphere is N2.

[0082] First, the specific surface area of ​​hard carbon was obtained based on BET theory through N2 desorption testing, the true density of hard carbon was obtained through a true density meter, and the interlayer spacing of hard carbon was obtained based on Bragg's law through XRD diffraction. The results are shown in Table 1.

[0083] Furthermore, the hard carbon materials prepared in the various embodiments and comparative examples were used as negative electrode active materials for sodium-ion secondary batteries. According to a mass ratio of 92%:3%:1.5%:3.5%, 184 mg of the above-mentioned hard carbon powder, 6 mg of conductive carbon black, 6 mg of a 2% (w / w) carboxymethyl cellulose solution, and 17.5 mg of a 40% (w / w) styrene-butadiene rubber were weighed out, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. This slurry was then uniformly coated onto the surface of a copper (Cu) foil using a 100 μm scraper. The slurry was dried in a 105°C forced-air drying oven for 2 hours. The Cu foil containing the active material was then cut into circular negative electrode sheets and transferred to a glove box for later use.

[0084] The simulated battery assembly was carried out in a MIKROUNA glove box filled with Ar atmosphere. A prepared carbon electrode was used as the negative electrode, a commercial electrolyte of 1 mol / L NaPF6 in DME was used as the electrolyte, and a Na metal sheet was used as the counter electrode to assemble a 2016 coin cell. After the battery was left to stand for 12 hours, the first charge-discharge test was conducted at a rate of 0.1 C, with a voltage range of 0–2 V. Rate charge-discharge tests were then conducted at a rate of 3 C. The test results are shown in Table 1.

[0085] Table 1 In summary, as shown in Table 1, the alkaline boiling treatment in this application removes some lignin from bamboo shavings, effectively inhibiting excessive graphitization of hard carbon materials. This not only increases the carbon interlayer spacing and shortens the carbon domain size but also promotes the formation of more closed-pore structures, thereby significantly improving the reversible capacity and ion transport kinetics of hard carbon materials. In addition, the filtrate produced by alkaline boiling is rich in lignin and contains a small amount of polysaccharides and hemicellulose. When used for subsequent coating treatment, these substances can coordinate the formation of long-range graphite domains with large interlayer spacing. This structure can induce the formation of a thin and robust solid electrolyte interface film during battery charging and discharging, while also facilitating efficient ion conduction. Ultimately, this results in higher first coulombic efficiency and superior kinetic performance of bamboo-based hard carbon materials, comprehensively improving the electrochemical performance of the materials and laying the foundation for their commercial application in sodium-ion battery anodes.

[0086] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0087] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing bamboo-based hard carbon material, characterized in that, include: Bamboo-based material is mixed with 2-4 wt% alkaline solution at a mass ratio of 1:5, boiled for 1-2 hours, and then naturally cooled to room temperature. Solid-liquid separation is achieved by pressure filtration. The resulting filtrate is sealed and stored for later use. The filter residue is washed with deionized water until neutral, dried, and then stored for later use. The dried filter residue is pre-carbonized, and the pre-carbonized product is crushed by an air jet mill and then pickled. The pickled product is filtered, washed with deionized water until neutral, and dried to obtain the pickled material. The pickled material is subjected to high-temperature carbonization treatment and then cooled to obtain bamboo-based hard carbon material.

2. The method for preparing bamboo-based hard carbon material according to claim 1, characterized in that, The pickled material is subjected to high-temperature carbonization treatment, and after cooling, bamboo-based hard carbon material is obtained, comprising: The pickling material and the filtrate stored in claim 1 are stirred and mixed at a mass ratio of 1:10-20. The pH value of the mixture is adjusted to 5-7 so that lignin in the filtrate precipitates and uniformly coats the surface of the bamboo charcoal. Then, the solid and liquid are separated by pressure filtration. The resulting filter cake is washed and dried to obtain the coated material. The coated material is subjected to high-temperature carbonization treatment, and after cooling, bamboo-based hard carbon material is obtained.

3. The method for preparing bamboo-based hard carbon material according to claim 1, characterized in that, The pre-carbonization conditions were as follows: pre-carbonization temperature of 400-600℃, heating rate of 5℃ / min, pre-carbonization time of 2 h, under N2 / Ar atmosphere.

4. The method for preparing bamboo-based hard carbon material according to claim 1, characterized in that, Air jet milling was used to crush the particles, with the particle size D50 controlled at 5±0.5μm.

5. The method for preparing bamboo-based hard carbon material according to claim 1, characterized in that, The pickling conditions were as follows: the pickling solution was 1 M hydrochloric acid solution, the material-to-liquid ratio was 1:5, the pickling temperature was 80℃, and the pickling time was 12 h.

6. The method for preparing bamboo-based hard carbon material according to claim 2, characterized in that, The pH value can be adjusted to 5-7 using one or more of the following: carbon dioxide, hydrochloric acid, acetic acid, citric acid, sulfuric acid, nitric acid, and oxalic acid.

7. The method for preparing bamboo-based hard carbon material according to claim 1 or 2, characterized in that, The high-temperature carbonization conditions were as follows: carbonization temperature of 1100-1300℃, carbonization time of 3 h, heating rate of 2℃ / min, and N2 / Ar atmosphere.

8. The method for preparing bamboo-based hard carbon material according to claim 1 or 2, characterized in that, The alkaline solution is either potassium hydroxide solution or sodium hydroxide solution.

9. A bamboo-based hard carbon material, characterized in that, The bamboo-based hard carbon material is prepared by the preparation method of bamboo-based hard carbon material according to any one of claims 1-8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the bamboo-based hard carbon material as described in claim 9.

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