Biomass hard carbon as well as preparation method and application thereof

Abstract

The invention discloses biomass hard carbon and a preparation method and application thereof, and belongs to the technical field of carbon material preparation. The preparation method of the biomass hard carbon comprises the following steps: providing a dissolving solution of cellulose / chitin; adding the waste biomass into the dissolved solution, and stirring to obtain a solution dissolved with cellulose / chitin; directly adding a pickling solution for pickling to obtain regenerated cellulose / chitin; finally, pre-oxidation crosslinking and high-temperature carbonization are conducted, and the biomass hard carbon is prepared. According to the invention, the crystallinity of the regenerated cellulose is regulated and controlled, and a crystalline region and an amorphous region of the regenerated cellulose are reasonably matched, so that the derived biomass hard carbon has rich closed-cell structures and closed-cell rate and brings excellent electrochemical performance to a sodium-ion battery as a negative electrode material. The preparation method is mild in treatment condition and simple in treatment process, does not need to consume a large amount of acid and alkali, and has the advantages of high efficiency, economy and environmental friendliness.

Description

Technical Field

[0001] The present application belongs to the technical field of carbon material preparation, and specifically relates to a method for preparing biomass hard carbon and the prepared biomass hard carbon, and also relates to the application of the biomass hard carbon as a negative electrode material in sodium ion batteries. Background Art

[0002] With the accelerated industrialization of sodium-ion batteries, developing 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) are subject to high costs, complex processes, and poor sustainability.

[0003] At the same time, 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, and waste paper products), are rich in natural cellulose. In addition, crustacean waste (such as lobster shells and crab shells) are rich in chitin, making them potential as raw materials for preparing hard carbon. However, the current treatment methods for 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 approaches reported in the field for waste biomass: 1. Dissolving the lignin and hemicellulose in the waste biomass and carbonizing the resulting biomass material (e.g., Chinese patent applications with publication numbers CN116770611A and CN119735194A); and 2. Dissolving the cellulose in the waste biomass and carbonizing the biomass material, leaving the lignin and hemicellulose (e.g., Chinese patent application with publication number CN118929622A). These existing solutions either fail to achieve targeted cellulose extraction, resulting in insufficient cellulose content in the hard carbon material; or they involve complex processes that may introduce impurities. Furthermore, they suffer from high energy consumption, complex processes, and high costs. Summary of the Invention

[0005] In view of this, the primary purpose of this application is to provide a method for preparing biomass hard carbon, which can realize the directional preparation of waste biomass into high-performance hard carbon negative electrode materials, and the preparation method is efficient, economical, and environmentally friendly, and can simultaneously solve the dual needs of resource recycling and battery material cost reduction and efficiency improvement.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions: One aspect of the present application discloses a method for preparing biomass hard carbon, comprising the following steps: providing a dissolving solution of cellulose / chitin; Adding waste biomass into the dissolving solution and stirring to dissolve the cellulose / chitin in the waste biomass to obtain a solution containing dissolved cellulose / chitin; The solution containing cellulose / chitin is directly added into an acid washing solution for acid washing to obtain regenerated cellulose / chitin; The regenerated cellulose / chitin is sequentially subjected to pre-oxidation cross-linking and high-temperature carbonization to prepare biomass hard carbon.

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

[0008] Another aspect of the present application discloses a sodium ion battery negative electrode material containing the biomass hard carbon described above.

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

[0010] Beneficial effects of this application: The preparation method of biomass hard carbon disclosed in the present application utilizes a cellulose / chitin dissolving solution to efficiently dissolve the cellulose / chitin in waste biomass, thereby destroying the crystalline region of the original cellulose / chitin, rearranging the macromolecules, weakening the intermolecular forces, and reducing the degree of recrystallization; at the same time, the cellulose / chitin is partially degraded in the cellulose / chitin dissolving solution, and some macromolecular chains are broken into small molecules, resulting in a decrease in the intermolecular forces and a decrease in the crystallinity. The cellulose / chitin is treated with a cellulose / chitin dissolving solution for different time periods, and the change in its crystallinity can be controlled or regulated during regeneration. The hard carbon subsequently prepared and derived has a rich closed-pore structure and closed-pore ratio, thereby obtaining excellent sodium storage performance and cyclic stability.

[0011] This biomass hard carbon has a rich closed-pore structure and closed-pore rate. 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0015] Figure 4These are the charge and discharge curves of the button batteries assembled with biomass hard carbon in Examples 1 to 10.

[0016] Figure 5 These are the charge and discharge curves of the button batteries assembled with biomass hard carbon in Comparative Examples 1 to 3. DETAILED DESCRIPTION

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

[0018] The first aspect of the present application discloses a method for preparing biomass hard carbon, comprising the following steps: providing a dissolving solution of cellulose / chitin; Adding waste biomass into the dissolving solution and stirring to dissolve the cellulose / chitin in the waste biomass to obtain a solution containing dissolved cellulose / chitin; The solution containing cellulose / chitin is directly added into an acid washing solution for acid washing to obtain regenerated cellulose / chitin; The regenerated cellulose / chitin is sequentially subjected to pre-oxidation cross-linking and high-temperature carbonization to prepare biomass hard carbon.

[0019] The applicant's research has found that crystallinity is crucial for biomass hard carbon derived from cellulose / chitin. Cellulose / chitin with high crystallinity (crystallinity > 60%) may over-graphitize during pyrolysis if the carbonization temperature is too high. Cellulose / chitin with moderate crystallinity (40% ≤ ≤ 60%) can decompose and carbonize during pyrolysis to produce long graphene sheets that serve as the walls of closed pores, which shrink to form a closed pore structure. Cellulose / chitin precursors with low crystallinity (crystallinity < 40%) exhibit few closed pores and abundant open pores (micropores and mesopores). The long graphite-like layers produced by the decomposition of crystalline cellulose / chitin serve as closed pore walls, while the non-crystalline regions act as inhibitors to prevent excessive graphitization of the carbon layers during high-temperature carbonization and also serve as active sites for the formation of closed pores.

[0020] Based on this, the applicant has provided a new method for preparing biomass hard carbon. This method utilizes cellulose / chitin dissolution technology to efficiently dissolve cellulose / chitin from waste biomass. After acid washing and regeneration, the biomass hard carbon is prepared through pre-oxidation and high-temperature carbonization. By controlling the treatment time of the cellulose / chitin dissolution solution on the cellulose / chitin, the change in its crystallinity during regeneration is controlled, resulting in a derived biomass hard carbon with a rich closed-pore structure and closed-pore ratio, thereby achieving excellent sodium storage performance and cyclic stability.

[0021] In the present application, the cellulose / chitin dissolving solution is a cellulose / chitin dissolving system commonly used in the art, and specific examples include 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, tetranitrogen tetraoxide / dimethylformamide system, paraformaldehyde / dimethyl sulfoxide system, phosphoric acid / polyphosphoric acid composite solvent system, NMMO / H20 solvent system, ionic liquid dissolving system, sodium hydroxide / urea / thiourea / water system, and one of ZnCl3 / water solvent systems, but are not limited thereto. In some examples, the cellulose / chitin dissolving solution is a copper ammonia solution, a copper ethylenediamine solution, or a ZnCl3 / water solvent system.

[0022] The preparation of the dissolving solution may refer to methods known in the art without any particular limitation.

[0023] As an example, a copper ammonia solution is prepared as follows: A 10-20 wt% copper salt solution and a 5-15 wt% alkali solution undergo a chemical reaction to generate a copper hydroxide precipitate. After separating and washing the precipitate, 15-25 wt% ammonia water is added dropwise until the precipitate dissolves. The copper salt solution is selected from an aqueous solution of a soluble copper salt, specific examples of which include but are not limited to at least one of copper nitrate, copper sulfate, and copper chloride. The alkali solution is selected from an aqueous solution of an alkali, specifically selected from conventional alkalis in the art, specific examples of which include but are not limited to at least one of lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0024] As another example, a copper ethylenediamine solution is prepared as follows: 10-20wt% copper salt solution and 5-15wt% alkali solution undergo a chemical reaction to generate copper hydroxide precipitate. After separating and washing the precipitate, take an appropriate amount of copper hydroxide precipitate in a beaker, add a small amount of distilled water to make it into a paste, and then slowly add anhydrous ethylenediamine while stirring with a glass rod until the copper hydroxide is completely dissolved. Wherein, the copper salt solution is selected from an aqueous solution of a soluble copper salt, and specific examples of the soluble copper salt include but are not limited to at least one of copper nitrate, copper sulfate, and copper chloride. The alkali solution is selected from an aqueous solution of an alkali, and the alkali is specifically selected from conventional types in the art, and specific examples include but are not limited to at least one of lithium hydroxide, sodium hydroxide, and potassium hydroxide. In addition, the preparation methods of cadmium ethylenediamine, nickel ethylenediamine, cobalt ethylenediamine, and zinc ethylenediamine solutions are similar to those of copper ethylenediamine.

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

[0026] Using copper ammonia or copper ethylenediamine solutions as examples, the principles of their dissolution and control of cellulose / chitin crystallinity are explained. Other dissolving solutions exhibit similar dissolution mechanisms, so these details are omitted here. Copper ammonia / copper ethylenediamine solutions are highly effective in dissolving cellulose / chitin. This dissolution mechanism is primarily based on the coordination of the copper ammonia / copper ethylenediamine complex with the hydroxyl (-OH) groups on the cellulose / chitin chains, weakening intermolecular forces and disrupting hydrogen bonds between cellulose / chitin molecules, enabling dissolution. Regeneration with copper ammonia / copper ethylenediamine yields regenerated cellulose / chitin with controlled, reduced crystallinity. This mechanism occurs when the copper ammonia / copper ethylenediamine solution penetrates the crystalline regions of the original cellulose / chitin, disrupting them and causing macromolecular rearrangement. This weakens intermolecular forces and reduces the degree of recrystallization. Furthermore, cellulose / chitin undergoes partial degradation in the copper ammonia / copper ethylenediamine solution, breaking some macromolecular chains into smaller molecules. This weakens intermolecular forces and reduces crystallinity. By treating cellulose / chitin with a dissolving solution for different periods of time, controllable changes in its crystallinity can be achieved, so that the subsequently derived hard carbon has a rich closed-pore structure and closed-pore rate.

[0027] In the present 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 agricultural waste containing cellulose, and specific examples of the agricultural waste include at least one of pine, poplar, bamboo, coconut shell, flax, ramie, bagasse, rice straw, and wheat straw, but are not limited thereto.

[0029] In other examples, the waste biomass may also be chemical waste containing cellulose. Specific examples of the 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 crustacean waste containing chitin. Specific examples of the crustacean waste include at least one of shrimp, crab, and shellfish shells, but are not limited thereto.

[0031] In the present application, the stirring of the waste biomass and the dissolved solution is carried out under conditions of -20°C to 30°C, for example, it can be any temperature of -20°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C or any range value therebetween.

[0032] In the present 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 that the cellulose / chitin in the waste biomass is completely dissolved; on the other hand, the amount of solution should not be too much. Firstly, it will cause waste, and secondly, excessive solution will increase the reaction rate. At the same time, the ratio of the two also needs to comprehensively consider the solubility of the dissolving solution, so the specific ratio is not particularly limited. In some specific examples of the present application, the mass ratio of the waste biomass to the dissolving solution is 1: (4~15), for example, it can be any mass ratio of 1:4, 1:5, 1:6, 1:8, 1:10, 1:12, 1:15, or a range of any two of them.

[0033] In the present application, by controlling the dissolution time, the crystallinity of the regenerated cellulose is regulated, so that it is converted from the original type I cellulose to type II cellulose, and the crystalline and non-crystalline regions of the regenerated cellulose are reasonably matched (preferably controlled to be moderately crystallinity, i.e., 40% ≤ crystallinity ≤ 60%), so that the subsequently derived biomass hard carbon has a rich closed-pore structure and closed-porosity, and a negative electrode material with excellent electrochemical performance can be obtained. In some examples, the stirring and dissolving time is 0.5 to 12 hours, for example, it can be any time of 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 11 hours, 12 hours, or any range between two times.

[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 acid washing, the steps of filtering, washing with water and drying are further included.

[0036] The water washing is stopped when the pH value of the filtrate reaches 6 to 8. The drying temperature is 50 to 90°C.

[0037] In this application, the pre-oxidation and cross-linking process is a conventional process for preparing biomass hard carbon, and its specific parameters are not particularly limited. In some examples, the pre-oxidation and cross-linking temperature is 150-300°C, the holding time is 0.5-12 hours, and the heating rate is 0.5-10°C / min.

[0038] In this application, high-temperature carbonization is also a conventional process for preparing biomass hard carbon. Carbonization refers to the process of thermally decomposing the organic components in the raw materials under anaerobic or oxygen-free conditions through thermochemical conversion, removing volatile substances, and converting them into carbon-rich solid products. Specific reaction temperature and other conditions can be determined through experimental methods. In some examples, the carbonization temperature is 1100-1500°C, the holding time is 0.5-4 hours, and the heating rate is 0.5-10°C / min.

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

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

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

[0042] It is understood that the negative electrode material for sodium ion batteries may also contain functional additives such as conductive agents and binders, which are conventional in the art and therefore are not particularly limited. For sodium ion batteries, it also includes components such as positive electrodes, separators, and electrolytes, which can all be conventional in the art without particular limitation. These will not be detailed here.

[0043] The present application is further illustrated below with reference to specific embodiments. It should be noted that the following specific embodiments are only for illustrative purposes 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 those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

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

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

[0047] (2) Regeneration of cellulose: at 20°C, waste cotton and the copper ammonia solution prepared in step (1) were mixed in a mass ratio of 1 kg:10 kg and stirred for 8 h to obtain a uniform 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.

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

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

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

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

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

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

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

[0058] Example 5 This embodiment discloses another method for preparing biomass hard carbon, and the specific steps are as follows: (1) Preparation of copper ethylenediamine solution: A 15 wt% copper sulfate aqueous solution and a 10 wt% sodium hydroxide aqueous solution are chemically reacted to generate a copper hydroxide precipitate. After separating and washing the precipitate, an appropriate amount of the 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 a copper ethylenediamine solution.

[0059] (2) Regeneration of cellulose: at 20°C, waste cotton and the copper ethylenediamine solution prepared in step (1) were mixed in a mass ratio of 1 kg:10 kg and stirred for 8 h to obtain a uniform 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, and the specific steps are as follows: (1) Preparation of zinc chloride solution: Add 60 g of zinc chloride solid to a beaker containing 40 mL of distilled water and stir continuously with a glass rod to help the zinc chloride dissolve evenly to prepare a zinc chloride solution.

[0062] (2) Regeneration of cellulose: at 20°C, waste cotton and the zinc chloride solution prepared in step (1) were mixed in a mass ratio of 1 kg:10 kg and stirred for 8 h to obtain a uniform 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.

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

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

[0065] (2) Regeneration of cellulose: The same as the implementation method of Example 1, except that: dilute sulfuric acid with a concentration of 10% is used for pickling.

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

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

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

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

[0070] Example 9 This embodiment discloses another method for preparing biomass hard carbon, and the specific steps 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 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 the temperature for 5 hours.

[0073] Example 10 This embodiment discloses another method for preparing biomass hard carbon, and the specific steps 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 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 the temperature for 3 hours.

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

[0077] (2) Regeneration of cellulose: The same as the implementation method of Example 1, except that the stirring of the waste cotton and the 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, and the specific steps are as follows: (1) Preparation of copper ammonia solution: refer to Example 1.

[0080] (2) Regeneration of cellulose: The same as the embodiment 1, except that the stirring of the waste cotton and the 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, and the specific steps are as follows: (1) Preparation of copper ammonia solution: refer to Example 1.

[0083] (2) Regeneration of cellulose: The same implementation as in Example 1, except that the mass ratio of waste cotton to 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, and the specific steps are as follows: (1) Preparation of copper ammonia solution: refer to Example 1.

[0086] (2) Regeneration of cellulose: The same implementation as in Example 1, except that the mass ratio of waste cotton to 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, using the same method as Example 1, except that the waste cotton is not subjected to dissolution and regeneration. The specific steps are as follows: Preparation of biomass hard carbon: Place untreated waste cotton directly in a muffle furnace, heat it to 225°C at a heating rate of 5°C / min, and keep it warm for 2 hours for pre-oxidation; place the pre-oxidized cellulose in a high-temperature furnace, heat it to 1300°C at a heating rate of 5°C / min, and keep it warm 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, using the same method as Example 1, except that the mixing time of the waste cotton and the 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 20 h.

[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, and the specific steps are as follows: (1) Preparation of copper ammonia solution: refer to Example 1.

[0093] (2) Obtaining biomass powder: The same as Example 1, except that the solution containing 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 test: XRD characterization was performed on the biomass hard carbon prepared in the examples and comparative examples. The characterization results are shown in Table 1. Figure 2 The XRD spectra of biomass hard carbon in Example 1 and Comparative Example 2 are shown in FIG.

[0096] Table 1 XRD test results

[0097] pass Figure 1It can be seen from the results that the (110) peaks at around 12.1° and 19.8° and the (020) peaks at around 22° in the XRD curves of Example 1 and Comparative Example 2 have significantly different characteristics. By calculation, we can obtain that the crystallinity of Example 1 is 50.8%, and the crystallinity of Comparative Example 2 is 32.8%. This is because as time changes during the process of dissolving cellulose in the copper ammonia solution, the cellulose begins to depolymerize and dissolve into the solution, resulting in the decomposition and disorder of the cellulose chains. However, when the dissolution time is too long, the cellulose chains will break, resulting in a significant decrease in crystallinity and cellulose chain length. After further treatment for 20 hours, the crystallinity dropped from 50.8% to 32.8% compared to the treatment for 8 hours. At this time, the crystallinity of the regenerated cellulose will also decrease accordingly.

[0098] The crystalline cellulose content is crucial for achieving a closed pore structure during the carbonization process. The decomposition of crystalline cellulose is carbonized to generate long graphene sheets as the walls of the closed pores, which shrink to form a closed pore structure. At the same time, the non-crystalline region components are not only active sites for the formation of closed pores, but also a barrier to prevent the graphitization tendency of regenerated cellulose / chitin-derived carbon. The regenerated cellulose precursor with low crystallinity cellulose shows few closed pores and abundant open pores (micropores and mesopores). The closed pore volume of Comparative Example 1 with high crystallinity is 0.82 cm 3 g -1 The closed pore volume of Comparative Example 2 with low crystallinity is 0.75 cm 3 g -1 The closed porosity is 25.6%. The closed pore volume of Experiment 1 with moderate crystallinity is 1.98 cm 3 g -1 , and the closed porosity is 45.2%. It has a rich closed pore structure and shows a high sodium storage capacity. Therefore, a suitable content of crystalline cellulose is required to form closed pores in biomass-derived hard carbon. The crystallinity and closed porosity in Comparative Example 3 are both lower than those in Example 1. One reason is that the solution in the prior art is different from that in the present application, and the other is that it needs to be combined with a specific cellulose dissolving agent and a specific dissolution process, while the process of the present application is simpler and easier to implement.

[0099] 2. TEM characterization: Figure 3 Transmission electron microscopy images of the biomass hard carbons from Example 1 and Comparative Example 2 are shown in Figure 2. As can be seen, Example 1 exhibits abundant nanopores, with abundant long graphite-like layers and a large number of closed pores, which accumulate to form closed interstitial domains in the turbine layer. The abundance of closed pores is related to its suitable crystallinity and cellulose content, which can be decomposed into long graphite-like layers during the carbonization process to surround and contract the sites. The microstructure of Comparative Example 2 is highly disordered, with difficulty identifying distinct closed pore regions and long graphite-like layers, and exhibiting a small number of nanopores.

[0100] 3. Electrochemical performance test 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 is mixed evenly with the conductive agent SuperP, the adhesive sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 8:1:0.5:0.5. An appropriate amount of water is added and stirred to form a slurry. The slurry is then evenly coated on the current collector copper foil. After drying, it is cut into circular pole pieces with a diameter of 14 mm. Under vacuum conditions, the pole pieces are blown dry at 80°C for about 3 hours and vacuum dried at 80°C for 6 hours. They are then transferred to a glove box for standby use. The battery is assembled in an Ar atmosphere glove box, using a metal sodium sheet as the counter electrode, 1 mol / L NaPF6 dissolved in DME solution as the electrolyte, and GF / D as the separator to form a CR2032 button cell.

[0101] The electrical performance of the assembled CR2032 button battery was tested with a charge current of 0.1C, a discharge current of 0.1C, and a charge and discharge voltage range of 0 to 2.0V. The test results are shown in Table 2. In addition, Figure 4 and Figure 5 The charge and discharge curves of the button batteries of Examples 1-10 and Comparative Examples 1-3 are shown in FIG.

[0102]

[0103] It can be seen from the test results in Table 2 that the biomass hard carbon prepared by the biomass hard carbon preparation method of the present application significantly improves the electrochemical properties of the material, while maintaining the first-cycle coulombic efficiency, improving the conductivity and rate performance (1C charging capacity) of the hard carbon material, and at the same time, the cycle performance is also increased to a certain extent.

[0104] For further information, see Figure 4 and Figure 5 The charge and discharge curve of the button battery prepared from the biomass hard carbon prepared in Example 1 shows typical hard carbon characteristics, with an initial charge capacity of 348.2 mAh / g and an initial charge and discharge efficiency of 91.2%. Compared with Comparative Examples 1-3, both the charge capacity and the initial charge and discharge efficiency are greatly improved.

[0105] In summary, thanks to the regulation of cellulose crystallinity by the preparation method in this application, the electrochemical properties of biomass hard carbon are significantly improved. In addition, the processing conditions of this application are mild, the processing process is simple, and does not require the consumption of large amounts of acid and alkali. It can also be carried out at room temperature, reducing pollution to the environment.

[0106] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing biomass hard carbon, characterized in that: The following steps are involved: providing a dissolving solution of cellulose / chitin; Adding waste biomass into the dissolving solution and stirring to dissolve the cellulose / chitin in the waste biomass to obtain a solution containing dissolved cellulose / chitin; The solution containing cellulose / chitin is directly added into an acid washing solution for acid washing to obtain regenerated cellulose / chitin; The regenerated cellulose / chitin is sequentially subjected to pre-oxidation cross-linking and high-temperature carbonization to prepare biomass hard carbon.

2. The preparation method according to claim 1, wherein The cellulose / chitin dissolving solution is one of a copper ammonia solution, a copper ethylenediamine solution, a cadmium ethylenediamine solution, a nickel ethylenediamine solution, a cobalt ethylenediamine solution, a zinc ethylenediamine solution, a carbon disulfide / sodium hydroxide system, a lithium chloride / N,N-dimethylacetamide system, a tetranitrogen tetroxide / dimethylformamide system, a paraformaldehyde / dimethyl sulfoxide system, a phosphoric acid / polyphosphoric acid composite solvent system, an NMMO / H20 solvent system, an ionic liquid dissolving system, a sodium hydroxide / urea / thiourea / water system, and a ZnCl3 / water solvent system.

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

4. The preparation method according to claim 1, wherein The stirring of the waste biomass and the dissolving solution is carried out at -20°C to 30°C, 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, wherein 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, wherein After acid washing, the process also includes filtering, washing with water and drying; Preferably, the water washing is stopped when the pH of the filtrate reaches 6-8; Preferably, the drying temperature is 50-90°C.

7. The preparation method according to claim 1, wherein The pre-oxidation cross-linking temperature is 150-300°C, the holding time is 0.5-12h, and the heating rate is 0.5-10°C / min; And / or, the high-temperature carbonization is carried out in a protective atmosphere, the carbonization temperature is 1100-1500° C., the holding time is 0.5-4 h, and the heating rate is 0.5-10° C. / min.

8. A biomass hard carbon, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7; Preferably, the closed pore volume of the biomass hard carbon is 0.05-0.15 cm 3 ·g -1 , the closed cell rate is 30-50%.

9. A sodium ion battery negative electrode material, characterized in that Contains the biomass hard carbon according to claim 8.

10. A sodium ion battery, characterized in that: Contains the sodium ion battery negative electrode material according to claim 9.

Images