Biomass hard carbon and preparation method and application thereof

Abstract

The application discloses biomass hard carbon and a preparation method and application thereof, and belongs to the technical field of carbon material preparation. The preparation of the biomass hard carbon comprises the following steps: providing a dissolving solution of cellulose / chitin; stirring waste biomass into the dissolving solution to obtain a solution in which cellulose / chitin is dissolved; then directly adding an acid washing solution to perform acid washing to obtain regenerated cellulose / chitin; and finally performing pre-oxidation crosslinking and high-temperature carbonization to prepare the biomass hard carbon. The application realizes regulation of the crystallinity of the regenerated cellulose, reasonably matches the crystalline region and the non-crystalline region of the regenerated cellulose, and thus the biomass hard carbon derived based on this has rich closed pore structures and a closed pore rate, and brings excellent electrochemical performance to a sodium ion battery as a negative electrode material. Moreover, the preparation method has the advantages of mild treatment conditions, a simple treatment process, no need to consume a large amount of acid and alkali, high efficiency, economy and environmental friendliness.

Description

Technical Field

[0001] This application belongs to the field of carbon material preparation technology, specifically relating to a method for preparing biomass hard carbon and the prepared biomass hard carbon, and also relating to the application of the biomass hard carbon as a negative electrode material in sodium-ion batteries. Background Technology

[0002] With the accelerated development of the sodium-ion battery industry, the development of low-cost, high-performance anode materials has become crucial. Hard carbon (HC) is considered an ideal anode material for sodium-ion batteries due to its suitable interlayer spacing and abundant sodium storage sites. However, traditional raw materials for preparing hard carbon (such as petrochemical derivatives and high-purity biomass) suffer from problems such as high cost, complex processes, or poor sustainability.

[0003] Meanwhile, a large amount of waste biomass, such as agricultural waste (straw, fruit shells, cotton, etc.) and waste cellulose-based materials (such as waste textiles, waste packaging materials, waste paper products, etc.), is rich in natural cellulose. In addition, crustacean waste (such as lobster shells, crab shells, etc.) is rich in chitin, which makes them potential raw materials for the preparation of hard carbon. However, the current methods for treating these waste biomass and crustacean waste are mainly incineration or landfill, which not only wastes resources but also exacerbates environmental pollution.

[0004] Currently, there are two main reported solutions for waste biomass in this field: ① dissolving lignin and hemicellulose in waste biomass and carbonizing the resulting biomass material (e.g., Chinese patent applications with publication numbers CN116770611A and CN119735194A); ② dissolving cellulose in waste biomass and carbonizing the resulting biomass material while retaining lignin and hemicellulose (e.g., Chinese patent application with publication number CN118929622A). These existing solutions either fail to achieve targeted extraction of cellulose, resulting in insufficient cellulose content in the hard carbon material; or the process is complex and may introduce impurities; furthermore, they also suffer from high energy consumption, complex processes, and high costs. Summary of the Invention

[0005] In view of this, the primary objective of this application is to provide a method for preparing biomass hard carbon, which enables the directional preparation of high-performance hard carbon anode materials from waste biomass. This method is efficient, economical, and environmentally friendly, and can simultaneously address the dual needs of resource recycling and cost reduction and efficiency improvement in battery materials.

[0006] To achieve the above objectives, this application adopts the following technical solution: One aspect of this application discloses a method for preparing biomass hard carbon, comprising the following steps: Provides a solution for dissolving cellulose / chitosan; Waste biomass is added to the dissolving solution and stirred to dissolve the cellulose / chitoxin in the waste biomass, resulting in a solution containing dissolved cellulose / chitoxin. The solution containing dissolved cellulose / chitosan is directly added to the acid washing solution for acid washing to obtain regenerated cellulose / chitosan. The regenerated cellulose / chitosan was subjected to pre-oxidative cross-linking and high-temperature carbonization in sequence to obtain biomass hard carbon.

[0007] Another aspect of this application discloses a biomass hard carbon prepared using the preparation method described above.

[0008] Another aspect of this application discloses a sodium-ion battery anode material containing the aforementioned biomass hard carbon.

[0009] Another aspect of this application discloses a sodium-ion battery containing the sodium-ion battery negative electrode material described above.

[0010] The beneficial effects of this application are: The method for preparing biomass hard carbon disclosed in this application utilizes a cellulose / chitosan dissolving solution to efficiently dissolve cellulose / chitosan in waste biomass. This disrupts the crystalline regions of the original cellulose / chitosan, causing macromolecular rearrangement, weakening intermolecular forces, and reducing the degree of recrystallization. Simultaneously, cellulose / chitosan undergoes partial degradation in the cellulose / chitosan dissolving solution, with some macromolecular chains breaking into smaller molecules, further reducing intermolecular forces and crystallinity. By treating cellulose / chitosan with the cellulose / chitosan dissolving solution for different durations, the changes in crystallinity can be controlled or regulated during regeneration. The resulting hard carbon possesses abundant closed-pore structures and a high closed-pore ratio, thereby achieving excellent sodium storage performance and cycle stability.

[0011] This biomass hard carbon has abundant closed-pore structure and closed-pore ratio. As a negative electrode material for sodium-ion batteries, it can improve the conductivity and rate performance of sodium-ion batteries while maintaining the first-cycle coulombic efficiency, thereby improving the cycle performance of sodium-ion batteries. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of the biomass hard carbon preparation method of this application.

[0013] Figure 2 The XRD patterns are those of the biomass hard carbon prepared in Example 1 and Comparative Example 2.

[0014] Figure 3 These are TEM images of the biomass hard carbon prepared in Example 1 and Comparative Example 2.

[0015] Figure 4The above are charge-discharge curves of the button batteries assembled from biomass hard carbon in Examples 1-10.

[0016] Figure 5 Charge-discharge curves of button batteries assembled from biomass hard carbon in Comparative Examples 1-3. Detailed Implementation

[0017] The embodiments of this application will be clearly and completely described below. The technical solutions in the embodiments described below are exemplary and only possible technical implementations of this application, not all possible implementations. Those skilled in the art can combine the embodiments of this application to obtain other embodiments without creative effort, and these embodiments are also within the protection scope of this application.

[0018] The first aspect of this application discloses a method for preparing biomass hard carbon, comprising the following steps: Provides a solution for dissolving cellulose / chitosan; Waste biomass is added to the dissolving solution and stirred to dissolve the cellulose / chitoxin in the waste biomass, resulting in a solution containing dissolved cellulose / chitoxin. The solution containing dissolved cellulose / chitosan is directly added to the acid washing solution for acid washing to obtain regenerated cellulose / chitosan. The regenerated cellulose / chitosan was subjected to pre-oxidative cross-linking and high-temperature carbonization in sequence to obtain biomass hard carbon.

[0019] The applicant's research found that crystallinity is crucial for cellulose / chitosan-derived biomass hard carbon. Cellulose / chitosan with excessively high crystallinity (>60%) may over-graphitize during pyrolysis if the carbonization temperature is too high. Cellulose / chitosan with moderate crystallinity (40% ≤ crystallinity ≤ 60%) can decompose and carbonize during pyrolysis to form long graphene sheets that act as walls for closed pores, shrinking to form closed-pore structures. Conversely, cellulose / chitosan precursors with excessively low crystallinity (<40%) exhibit few closed pores and abundant open pores (micropores and mesopores). The long graphitic layers produced by the decomposition of crystalline cellulose / chitosan act as walls for closed pores, while the amorphous regions act as inhibitors of excessive graphitization of the carbon layers during high-temperature carbonization, and also serve as active sites for forming closed pores.

[0020] Based on this, the applicant provides a novel method for preparing biomass hard carbon. Utilizing cellulose / chitosan dissolution technology, cellulose / chitosan in waste biomass is efficiently dissolved. After acid washing and regeneration, pretreatment oxidation and high-temperature carbonization are performed to obtain biomass hard carbon. By controlling the different treatment times of the cellulose / chitosan dissolution solution on cellulose / chitosan, the change in crystallinity during regeneration is controlled, resulting in biomass hard carbon with abundant closed-pore structures and high closed-pore ratio, thus achieving excellent sodium storage performance and cycle stability.

[0021] In this application, the cellulose / chitosan dissolving solution is a common cellulose / chitosan dissolving system in the art, specifically including, but not limited to, one of the following: copper ammonia solution, copper ethylenediamine solution, cadmium ethylenediamine solution, nickel ethylenediamine solution, cobalt ethylenediamine solution, zinc ethylenediamine solution, carbon disulfide / sodium hydroxide system, lithium chloride / N,N-dimethylacetamide system, tetraoxonium / dimethylformamide system, paraformaldehyde / dimethyl sulfoxide system, phosphoric acid / polyphosphoric acid composite solvent system, NMMO / H2O solvent system, ionic liquid dissolving system, sodium hydroxide / urea / thiourea / water system, and ZnCl3 / water solvent system. In some examples, the cellulose / chitosan dissolving solution is a copper ammonia solution, a copper ethylenediamine solution, or a ZnCl3 / water solvent system.

[0022] The preparation of the dissolving solution can be carried out in accordance with methods known in the art, without any particular limitations.

[0023] As an example, the preparation method of copper ammonia solution is as follows: A 10-20 wt% copper salt solution reacts chemically with a 5-15 wt% alkaline solution to form copper hydroxide precipitate. After separating and washing the precipitate, 15-25 wt% ammonia solution is added dropwise until the precipitate dissolves. The copper salt solution is selected from aqueous solutions of soluble copper salts, including but not limited to at least one of copper nitrate, copper sulfate, and copper chloride. The alkaline solution is selected from aqueous solutions of alkalis, specifically from conventional types in the art, including but not limited to at least one of lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0024] As another example, the preparation method of copper ethylenediamine solution is as follows: A 10-20 wt% copper salt solution reacts chemically with a 5-15 wt% alkaline solution to form copper hydroxide precipitate. After separating and washing the precipitate, a suitable amount of the copper hydroxide precipitate is placed in a beaker, and a small amount of distilled water is added to form a paste. Then, anhydrous ethylenediamine is slowly added while stirring with a glass rod until the copper hydroxide is completely dissolved. The copper salt solution is selected from aqueous solutions of soluble copper salts, including but not limited to at least one of copper nitrate, copper sulfate, and copper chloride. The alkaline solution is selected from aqueous solutions of alkalis, specifically from conventional types in the art, including but not limited to at least one of lithium hydroxide, sodium hydroxide, and potassium hydroxide. Furthermore, the preparation methods for cadmium ethylenediamine, nickel ethylenediamine, cobalt ethylenediamine, and zinc ethylenediamine solutions are similar to those for copper ethylenediamine.

[0025] It is understood that other cellulose / chitosan solutions, such as carbon disulfide / sodium hydroxide systems, lithium chloride / N,N-dimethylacetamide systems, tetraoxonium / dimethylformamide systems, paraformaldehyde / dimethyl sulfoxide systems, phosphoric acid / polyphosphoric acid composite solvent systems, NMMO / H2O solvent systems, ionic liquid dissolution systems, sodium hydroxide / urea / thiourea / water systems, ZnCl3 / water solvent systems, etc., can all be prepared by methods known in the art, and will not be elaborated here.

[0026] Taking cuprammonium or copper ethylenediamine solutions as examples, the principle of their dissolution and regulation of cellulose / chitosan crystallin crystallinity is explained. Other dissolving solutions have similar dissolution mechanisms and will not be elaborated upon. Cuprammonium / copper ethylenediamine solutions can efficiently dissolve cellulose / chitosan. The dissolution mechanism is mainly based on the coordination effect of the cuprammonium / copper ethylenediamine complex on the hydroxyl groups (-OH) on the cellulose / chitosan chains, weakening the intermolecular forces and thus breaking the hydrogen bonds between cellulose / chitosan molecules, allowing cellulose / chitosan to dissolve. After regeneration with cuprammonium / copper ethylenediamine, regenerated cellulose / chitosan with reduced and controllable crystallinity can be obtained. Specifically, the cuprammonium / copper ethylenediamine solution penetrates into the crystalline regions of cellulose / chitosan, destroying the original crystalline regions, causing macromolecular rearrangement, weakening intermolecular forces, and reducing the degree of recrystallization. In addition, cellulose / chitosan undergoes partial degradation in cuprammonium / copper ethylenediamine solutions, with some macromolecular chains breaking into smaller molecules, leading to reduced intermolecular forces and decreased crystallinity. By treating cellulose / chitin with a dissolving solution for different durations, the crystallinity can be controlled, resulting in hard carbon with abundant closed-pore structures and high closed-pore ratio.

[0027] In this application, the waste biomass may be at least one of waste textiles containing cellulose, waste packaging materials, waste decorative materials, and waste cotton.

[0028] In some examples, the waste biomass may also be cellulose-containing agricultural waste, and specific examples of such agricultural waste include at least one of pine wood, poplar wood, bamboo, coconut shell, flax, ramie, sugarcane bagasse, rice straw, and wheat straw, but are not limited thereto.

[0029] In other examples, the waste biomass may also be cellulose-containing chemical waste, and specific examples of such chemical waste include at least one of α-cellulose, β-cellulose, microcrystalline cellulose, and carboxymethyl cellulose, but are not limited thereto.

[0030] In other examples, the waste biomass may also be chitin-containing crustacean waste, and specific examples of the crustacean waste include at least one of the shells of shrimp, crab, and shellfish, but are not limited thereto.

[0031] In this application, the stirring of the waste biomass and the dissolving solution is carried out at a temperature of -20℃ to 30℃, for example, any temperature of -20℃, -10℃, -5℃, 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃ or any value between two of them.

[0032] In this application, the ratio of the dissolving solution to the waste biomass can be determined based on actual conditions or through experimental methods. Specifically, on the one hand, it is necessary to ensure that the waste biomass is fully immersed in the dissolving solution to ensure complete dissolution of cellulose / chitosan in the waste biomass; on the other hand, the amount of solution should not be too large, as this would lead to waste and an increased reaction rate. Furthermore, the ratio of the two also needs to take into account the solubility of the dissolving solution; therefore, there is no particular limitation on the specific ratio. In some specific examples of this application, the mass ratio of the waste biomass to the dissolving solution is 1:(4~15), for example, it can be any mass ratio or a range of both from 1:4, 1:5, 1:6, 1:8, 1:10, 1:12, 1:15.

[0033] In this application, the crystallinity of regenerated cellulose is regulated by controlling the dissolution time, transforming it from type I cellulose to type II cellulose. This results in a reasonable balance between crystalline and amorphous regions of the regenerated cellulose (preferably controlled at a moderate crystallinity, i.e., 40% ≤ crystallinity ≤ 60%). Consequently, the subsequently derived biomass hard carbon possesses a rich closed-pore structure and high closed-pore ratio, leading to a negative electrode material with excellent electrochemical performance. In some examples, the stirring and dissolution time is 0.5~12h, for example, any time from 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 8h, 10h, 11h, 12h, or any range between two values.

[0034] In some examples, the pickling solution is a hydrochloric acid or sulfuric acid solution with a mass concentration of 10% to 20%.

[0035] In some examples, after pickling, there are also steps of filtration, washing with water and drying.

[0036] The water washing is stopped when the pH of the filtrate reaches 6-8. The drying temperature is 50-90℃.

[0037] In this application, the pre-oxidative crosslinking is a conventional process for preparing biomass hard carbon, and its specific parameters are not particularly limited. In some examples, the pre-oxidative crosslinking temperature is 150~300℃, the holding time is 0.5~12h, and the heating rate is 0.5~10℃ / min.

[0038] In this application, the high-temperature carbonization described is also a conventional process for preparing biomass hard carbon. Carbonization refers to the process in which the organic components in the raw materials undergo thermal decomposition through thermochemical transformation under anaerobic or oxygen-deficient conditions, removing volatile substances and converting them into carbon-rich solid products. Specific reaction temperatures and other conditions can be determined experimentally. In some examples, the carbonization temperature is 1100~1500℃, the holding time is 0.5~4h, and the heating rate is 0.5~10℃ / min.

[0039] The second aspect of this application discloses a biomass hard carbon, which is prepared using the preparation method described in the first aspect of this application. In some examples of this application, the closed-cell volume of the biomass hard carbon is 0.05~0.15 cm³. 3 ·g -1 The closed-cell rate is 30-50%.

[0040] The third aspect of this application discloses a sodium-ion battery negative electrode containing the biomass hard carbon described in the second aspect of this application.

[0041] The fourth aspect of this application discloses a sodium-ion battery containing the sodium-ion battery negative electrode described in the third aspect of this application.

[0042] It is understandable that sodium-ion battery anode materials may also contain functional additives such as conductive agents and binders, all of which are conventional types in the field and therefore not particularly limited. Sodium-ion batteries also include components such as the cathode, separator, and electrolyte, all of which can be conventional types in the field without special restrictions. These will not be elaborated upon here.

[0043] The present application is further illustrated below with reference to specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present application in any way.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0045] In addition, unless otherwise specified, methods without detailed conditions or steps are conventional methods, and the reagents and materials used are commercially available.

[0046] Example 1 This embodiment discloses a method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: 15wt% copper sulfate aqueous solution and 10wt% sodium hydroxide aqueous solution are reacted to generate copper hydroxide precipitate. After separating and washing the precipitate, 20wt% ammonia water is added dropwise until the precipitate dissolves to prepare copper ammonia solution.

[0047] (2) Regeneration of cellulose: At 20°C, waste cotton and the copper ammonia solution prepared in step (1) are mixed and stirred for 8 hours at a mass ratio of 1 kg: 10 kg to obtain a homogeneous solution containing cellulose. The solution containing cellulose is directly added to 500 mL of dilute hydrochloric acid (concentration of 10%) for acid washing to obtain regenerated cellulose. The acid-washed regenerated cellulose is filtered, washed with water until the pH of the filtrate is 6~8, and then placed in a 60°C oven to dry to constant weight.

[0048] (3) Preparation of biomass hard carbon: The dried regenerated cellulose in step (2) is placed in a muffle furnace and heated to 225°C at a heating rate of 5°C / min and kept at the temperature for 2 hours for pre-oxidation; the pre-oxidized cellulose is placed in a high-temperature furnace and heated to 1300°C at a heating rate of 5°C / min and kept at the temperature for 2 hours to complete high-temperature carbonization and obtain biomass hard carbon material.

[0049] Example 2 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0050] (2) Regeneration of chitin: The same implementation method as in Example 1, except that the waste cotton is replaced with shrimp shells of equal mass.

[0051] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0052] Example 3 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0053] (2) Regeneration of cellulose: The same implementation method as in Example 1, except that the mixing time of waste cotton and copper ammonia solution is 0.5h.

[0054] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0055] Example 4 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0056] (2) Regeneration of cellulose: The same implementation method as in Example 1, except that the mixing time of waste cotton and copper ammonia solution is 12h.

[0057] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0058] Example 5 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ethylenediamine solution: 15wt% copper sulfate aqueous solution and 10wt% sodium hydroxide aqueous solution are reacted to generate copper hydroxide precipitate. After separating and washing the precipitate, an appropriate amount of copper hydroxide precipitate is placed in a beaker, a small amount of distilled water is added to make it into a paste, and then anhydrous ethylenediamine is slowly added while stirring with a glass rod until the copper hydroxide is completely dissolved to prepare copper ethylenediamine solution.

[0059] (2) Regeneration of cellulose: At 20°C, waste cotton and the copper ethylenediamine solution prepared in step (1) were mixed at a mass ratio of 1 kg: 10 kg and stirred for 8 hours to obtain a homogeneous solution containing cellulose. The solution containing cellulose was directly added to 500 mL of dilute hydrochloric acid (concentration of 10%) for acid washing to obtain regenerated cellulose. The acid-washed regenerated cellulose was filtered, washed with water until the pH of the filtrate was 6~8, and then dried in a 60°C oven to constant weight.

[0060] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0061] Example 6 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of zinc chloride solution: Add 60g of weighed zinc chloride solid to a beaker containing 40mL of distilled water, and stir continuously with a glass rod to help the zinc chloride dissolve evenly, thus preparing a zinc chloride solution.

[0062] (2) Regeneration of cellulose: At 20°C, waste cotton and zinc chloride solution prepared in step (1) are mixed and stirred for 8 hours at a mass ratio of 1 kg: 10 kg to obtain a homogeneous solution containing cellulose. The solution containing cellulose is directly added to 500 mL of dilute hydrochloric acid (concentration of 10%) for acid washing to obtain regenerated cellulose. The acid-washed regenerated cellulose is filtered, washed with water until the pH of the filtrate is 6~8, and then placed in a 60°C oven to dry to constant weight.

[0063] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0064] Example 7 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0065] (2) Regeneration of cellulose: The same as in Example 1, except that acid washing is performed using 10% dilute sulfuric acid.

[0066] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0067] Example 8 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0068] (2) Regeneration of cellulose: The method is the same as in Example 1, except that 15% dilute hydrochloric acid is used for acid washing.

[0069] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0070] Example 9 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0071] (2) Regeneration of cellulose: Refer to Example 1.

[0072] (3) Preparation of biomass hard carbon: The same implementation method as in Example 1, except that the pre-oxidation process is to heat to 200°C at a heating rate of 3°C / min and keep warm for 5 hours.

[0073] Example 10 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0074] (2) Regeneration of cellulose: Refer to Example 1.

[0075] (3) Preparation of biomass hard carbon: The same implementation method as in Example 1, except that the high-temperature carbonization process is to heat to 1500°C at a heating rate of 3°C / min and keep warm for 3 hours.

[0076] Example 11 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0077] (2) Regeneration of cellulose: The same implementation method as in Example 1, except that the stirring of waste cotton and copper ammonia solution is carried out at -20°C.

[0078] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0079] Example 12 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0080] (2) Regeneration of cellulose: The same implementation method as in Example 1, except that the stirring of waste cotton and copper ammonia solution is carried out at 30°C.

[0081] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0082] Example 13 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0083] (2) Regeneration of cellulose: The same implementation method as in Example 1, except that the mass ratio of waste cotton and copper ammonia solution is 1:4.

[0084] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0085] Example 14 This embodiment discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0086] (2) Regeneration of cellulose: The same implementation method as in Example 1, except that the mass ratio of waste cotton and copper ammonia solution is 1:15.

[0087] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0088] Comparative Example 1 This comparative example discloses another method for preparing biomass hard carbon, which adopts the same implementation method as Example 1, except that the waste cotton is not subjected to dissolution and regeneration treatment. The specific steps are as follows: Preparation of biomass hard carbon: Untreated waste cotton is placed directly in a muffle furnace and heated to 225°C at a heating rate of 5°C / min, and held for 2 hours for pre-oxidation; the pre-oxidized cellulose is placed in a high-temperature furnace and heated to 1300°C at a heating rate of 5°C / min, and held for 2 hours to complete high-temperature carbonization and obtain biomass hard carbon material.

[0089] Comparative Example 2 This comparative example discloses another method for preparing biomass hard carbon, which adopts the same implementation method as Example 1, except that the mixing time of waste cotton and copper ammonia solution is 20 hours. The specific steps are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0090] (2) Regeneration of cellulose: Refer to Example 1, except that the mixing time of waste cotton and copper ammonia solution is 20h.

[0091] (3) Preparation of biomass hard carbon: Refer to Example 1.

[0092] Comparative Example 3 This comparative example discloses another method for preparing biomass hard carbon, the specific steps of which are as follows: (1) Preparation of copper ammonia solution: Refer to Example 1.

[0093] (2) Obtaining biomass powder: Same as in Example 1, except that the solution containing dissolved cellulose is discarded and the biomass powder is retained. For details, please refer to the Chinese patent application with publication number CN118929622A.

[0094] (3) Preparation of biomass hard carbon: The biomass powder obtained in step (2) is placed in a muffle furnace and biomass hard carbon is prepared according to the implementation method in Example 1.

[0095] Performance testing 1. XRD Testing: The biomass hard carbon prepared in the examples and comparative examples was characterized by XRD. The characterization results are shown in Table 1. Furthermore, Figure 2 The XRD patterns of biomass hard carbon in Example 1 and Comparative Example 2 are shown in the figure.

[0096] Table 1 XRD Test Results

[0097] pass Figure 1The results show that the (110) peak at approximately 12.1° and 19.8° and the (020) peak at approximately 22° in the XRD curves of Example 1 and Comparative Example 2 have significantly different characteristics. Calculations show that the crystallinity of Example 1 is 50.8%, while that of Comparative Example 2 is 32.8%. This is because during the dissolution of cellulose in the copper ammonia solution, as time progresses, cellulose begins to depolymerize and dissolve into the solution, leading to the decomposition and disorder of the cellulose chains. However, if the dissolution time is too long, the cellulose chains will break, resulting in a significant decrease in crystallinity and cellulose chain length. Further treatment for 20 hours resulted in a decrease in crystallinity from 50.8% to 32.8% compared to treatment for 8 hours. At this point, the crystallinity of the regenerated cellulose also decreases accordingly.

[0098] The crystalline cellulose content is crucial for achieving a closed-pore structure during carbonization. The decomposition of highly crystalline cellulose, carbonized to form long graphene sheets, acts as the walls of the closed pores, which then shrink to form the closed-pore structure. Simultaneously, the amorphous regions not only serve as active sites for forming closed pores but also act as a barrier against the graphitization tendency of regenerated cellulose / chitosan-derived carbon. Regenerated cellulose precursors with low crystalline cellulose exhibit few closed pores and abundant open pores (micropores and mesopores). Comparative Example 1, with excessively high crystallinity, has a closed-pore volume of 0.82 cm³. 3 g -1 The closed-cell rate was 22.4%. The closed-cell volume of Comparative Example 2, with its low crystallinity, was 0.75 cm³. 3 g -1 The closed-cell rate was 25.6%. In Experiment 1, with moderate crystallinity, the closed-cell volume was 1.98 cm³. 3 g -1 The closed-pore ratio was 45.2%. It possesses abundant closed-pore structures, exhibiting high sodium storage capacity. Therefore, forming closed pores in biomass-derived hard carbon requires an appropriate amount of crystalline cellulose. The crystallinity and closed-pore ratio in Comparative Example 3 are both lower than those in Example 1. One reason is that the existing technology differs from this application; another is that it requires the use of a specific cellulose solvent and a specific dissolution process, while the process in this application is simpler and easier to implement.

[0099] 2. TEM characterization: Figure 3 The image shows transmission electron microscopy (TEM) images of biomass hard carbon from Example 1 and Comparative Example 2. It can be seen that Example 1 exhibits abundant nanopores, with rich, long graphite-like layers and numerous closed pores that accumulate therein to form turbine-like closed void domains. The abundance of closed pores is related to its suitable crystallinity and cellulose content, which can decompose into long graphite-like layers during carbonization to surround and shrink the sites. Comparative Example 2 has a highly disordered microstructure, with difficult-to-identify regions of closed pores and long graphite-like layers, and contains only a small number of nanopores.

[0100] 3. Electrochemical performance testing The biomass hard carbon in the examples and comparative examples was prepared into corresponding sodium-ion batteries according to the following method: Biomass-based hard carbon powder was mixed uniformly with conductive agent SuperP, binder sodium carboxymethyl cellulose, and styrene-butadiene rubber at a mass ratio of 8:1:0.5:0.5. A suitable amount of water was added and stirred to form a slurry. The slurry was then uniformly coated onto a current collector copper foil, dried, and cut into circular electrode sheets with a diameter of 14 mm. Under vacuum conditions, the electrode sheets were dried at 80°C with forced air for approximately 3 hours, followed by vacuum drying at 80°C for 6 hours. They were then transferred to a glove box for later use. Battery assembly was performed in an Ar atmosphere glove box, using a sodium metal sheet as the counter electrode, 1 mol / L NaPF6 dissolved in DME solution as the electrolyte, and GF / D as the separator, to assemble a CR2032 button cell.

[0101] The electrical performance of the assembled CR2032 button cells was tested, with a charging current of 0.1C, a discharging current of 0.1C, and a charge / discharge voltage range of 0–2.0V. The test results are shown in Table 2. Furthermore, Figure 4 and Figure 5 The charge-discharge curves of the button batteries in Examples 1-10 and Comparative Examples 1-3 are shown in the figure.

[0102]

[0103] As can be seen from the test results in Table 2, the biomass hard carbon prepared by the method of this application significantly improves the electrochemical performance of the material. While maintaining the first-cycle coulombic efficiency, it improves the conductivity and rate performance (1C charging capacity) of the hard carbon material, and the cycle performance is also increased to a certain extent.

[0104] For further details, please refer to [link / reference]. Figure 4 and Figure 5 The button battery prepared from biomass hard carbon in Example 1 exhibits typical hard carbon characteristics in its charge-discharge curve. The initial charge specific capacity is 348.2 mAh / g, and the initial charge-discharge efficiency is 91.2%. Compared with Comparative Examples 1-3, both the charge specific capacity and the initial charge-discharge efficiency are significantly improved.

[0105] In summary, thanks to the control of cellulose crystallinity in the preparation method of this application, the electrochemical performance of biomass hard carbon is significantly improved. Furthermore, the processing conditions of this application are mild, the process is simple, it does not require the consumption of large amounts of acid and alkali, and it can be carried out at room temperature, thus reducing environmental pollution.

[0106] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing biomass hard carbon, characterized in that, Includes the following steps: Provides a solution for dissolving cellulose / chitosan; Waste biomass is added to the dissolving solution and stirred to dissolve the cellulose / chitoxin in the waste biomass, resulting in a solution containing dissolved cellulose / chitoxin. The solution containing dissolved cellulose / chitosan is directly added to the acid washing solution for acid washing to obtain regenerated cellulose / chitosan with a crystallinity of 40%~60%. The regenerated cellulose / chitosan was subjected to pre-oxidative cross-linking and high-temperature carbonization in sequence to obtain biomass hard carbon.

2. The preparation method according to claim 1, characterized in that, The cellulose / chitosan dissolving solution is one of the following: copper ammonia solution, copper ethylenediamine solution, cadmium ethylenediamine solution, nickel ethylenediamine solution, cobalt ethylenediamine solution, zinc ethylenediamine solution, carbon disulfide / sodium hydroxide system, lithium chloride / N,N-dimethylacetamide system, tetraoxonium / dimethylformamide system, paraformaldehyde / dimethyl sulfoxide system, phosphoric acid / polyphosphoric acid composite solvent system, NMMO / H2O solvent system, ionic liquid dissolving system, sodium hydroxide / urea / thiourea / water system, and ZnCl3 / water solvent system.

3. The preparation method according to claim 1, characterized in that, The waste biomass is at least one of the following: waste textiles containing cellulose, waste packaging materials, waste decorative materials, and waste cotton. And / or, is a cellulose-containing agricultural waste, wherein the agricultural waste is at least one of pine wood, poplar wood, bamboo, coconut shell, flax, ramie, sugarcane bagasse, rice straw, and wheat straw; And / or, is a cellulose-containing chemical waste, wherein the chemical waste is at least one of α-cellulose, β-cellulose, microcrystalline cellulose, and carboxymethyl cellulose; And / or, is a crustacean waste containing chitin, wherein the crustacean waste is at least one of the shells of shrimp, crab, and shellfish.

4. The preparation method according to claim 1, characterized in that, The mixing of the waste biomass and the dissolving solution is carried out at -20℃ to 30℃, the mass ratio of the waste biomass to the dissolving solution is 1:(4~15), and the dissolving time is 0.5~12h.

5. The preparation method according to claim 1, characterized in that, The pickling solution is a hydrochloric acid or sulfuric acid solution with a concentration of 10% to 20%.

6. The preparation method according to claim 1, characterized in that, After pickling, the process also includes filtration, washing with water, and drying.

7. The preparation method according to claim 6, characterized in that, The water washing is stopped when the pH of the filtrate reaches 6-8.

8. The preparation method according to claim 6, characterized in that, The drying temperature is 50~90℃.

9. The preparation method according to claim 1, characterized in that, The pre-oxidative crosslinking temperature is 150~300℃, the holding time is 0.5~12h, and the heating rate is 0.5~10℃ / min; And / or, the high-temperature carbonization is carried out in a protective atmosphere, with a carbonization temperature of 1100~1500℃, a holding time of 0.5~4h, and a heating rate of 0.5~10℃ / min.

10. A type of biomass hard carbon, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

11. The biomass hard carbon as described in claim 10, characterized in that, The closed-cell volume of the biomass hard carbon is 0.05~0.15 cm³. 3 ·g -1 The closed-cell rate is 30-50%.

12. A sodium-ion battery anode material, characterized in that, Contains the biomass hard carbon as described in claim 10 or 11.

13. A sodium-ion battery, characterized in that, It contains the sodium-ion battery anode material as described in claim 12.

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