Preparation method of phyllostachys edulis derived hard carbon material and application of phyllostachys edulis derived hard carbon material in sodium-ion battery

Abstract

The invention discloses a preparation method of a moso bamboo derived hard carbon material and application of the moso bamboo derived hard carbon material in a sodium ion battery, and belongs to the technical field of new energy materials. Moso bamboo powder serves as a precursor, acid pickling pretreatment is conducted, then pre-carbonization is conducted at the temperature of 300-800 DEG C, secondary carbonization is conducted at the temperature of 1400-1500 DEG C after acid pickling purification, and the moso bamboo derived hard carbon material is obtained. And micropore closing and surface repairing are induced. By strictly limiting the technological process of low-temperature pre-carbonization, acid pickling and impurity removal and high-temperature reconstruction and hole closing, the contradiction that the biomass hard carbon material is large in specific surface area, low in first efficiency and insufficient in platform capacity is successfully solved. When being used as the negative electrode of the sodium ion battery, the composite material has the advantages of high reversible specific capacity (gt, 308mAh / g), high platform capacity ratio (gt, 53%) and high first charge-discharge efficiency (gt; the energy density and the cycling stability of the whole battery are remarkably improved, and a new way is provided for the development of a low-cost and high-performance sodium ion battery negative electrode material.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, and in particular relates to a method for preparing a bamboo-derived hard carbon material and its application in sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries, with their advantages of abundant sodium resources, low cost, and excellent low-temperature performance, have shown great application potential in large-scale energy storage and low-speed electric vehicles. Among anode materials, biomass-derived hard carbon is considered one of the most promising routes for industrialization due to its wide availability, diverse structures, and high sodium storage capacity.

[0003] Moso bamboo, as a typical high-yield biomass, possesses a unique hierarchical vascular bundle structure and high cellulose content, making it an excellent precursor for hard carbon production. However, moso bamboo contains a certain amount of inorganic impurities (such as silicon, potassium, and calcium), and due to the dense structure of its fibers, these impurities are often deeply encapsulated within the organic matrix. Existing technologies for preparing hard carbon anodes using moso bamboo mainly face the following bottlenecks:

[0004] 1) The contradiction between impurity removal and structure preservation: Traditional preparation processes typically employ either "direct acid washing of raw materials" or "one-step high-temperature carbonization." If direct acid washing is used, the biomass structure of bamboo is extremely dense due to the lack of pyrolysis treatment, making it difficult for acid to penetrate the fiber bundles and resulting in incomplete removal of deep impurities (especially silicates). These residual impurities will undergo side reactions with carbon during subsequent high-temperature carbonization, reducing the material's conductivity and sodium storage activity.

[0005] 2) If a one-step high-temperature carbonization is used, the carbon skeleton will rapidly shrink and graphitize as the temperature rises, "locking" impurities inside the carbon layer, making them equally difficult to remove. In addition, the presence of impurities can catalyze graphitization or cause pore blockage, hindering the formation of closed pores.

[0006] High capacity and high first-efficiency are difficult to achieve simultaneously: To increase capacity, existing technologies often employ strong chemical activation (such as KOH activation) to create pores. While this method increases sodium storage sites, it also generates a huge specific surface area (typically >1000 m²). 2 The battery has a large number of open pores (g) and electrolytes. This causes the electrolyte to decompose on the large surface area during the first charge and discharge cycle, forming an excessively thick SEI film. This consumes a large amount of active sodium source, resulting in an extremely low initial coulombic efficiency (ICE) (typically below 80%), which severely limits the energy density of the entire battery.

[0007] The mechanism for regulating the closed-pore structure remains unclear: The high plateau capacity of hard carbon primarily stems from the pore-filling mechanism (i.e., sodium ions filling the closed micropores). However, current processes lack precise control over the structure-property relationship between pre-carbonization temperature and micropore evolution. If the pre-carbonization temperature is too low, the pores remain closed, resulting in incomplete impurity removal; if the pre-carbonization temperature is too high, the pores collapse or close prematurely, preventing the formation of effective closed-pore volume. Existing processes often struggle to find a process window that adequately exposes impurities for cleaning while preserving sufficient framework for high-temperature reconstruction of closed pores.

[0008] Therefore, there is an urgent need to develop a method for preparing bamboo-derived hard carbon that can precisely control the carbonization process, thoroughly remove deep impurities, and induce the formation of a low-defect, high-closed-pore microstructure without pore-forming agents and at low cost, so as to achieve a synergistic improvement in high reversible capacity, high initial efficiency, and high plateau capacity ratio. Summary of the Invention

[0009] To address the shortcomings of existing biomass hard carbon materials (especially those using bamboo precursors) in sodium storage performance (currently, most bamboo carbon materials primarily utilize slope-based sodium storage) and the insufficient depth of research on the correlation between precursors, processes, structures, and performance, this invention provides a method for preparing bamboo-derived hard carbon materials and their application in sodium-ion batteries. This invention aims to provide a deeply optimized preparation method that, by strictly limiting the pre-carbonization-acid washing-reconstruction process window, constructs a unique low-defect, multi-closed-pore structure in bamboo-based hard carbon, thus preparing a high-performance hard carbon anode material. This method, through carefully designed pretreatment processes and precisely controlled carbonization / post-treatment processes, fully utilizes the natural structural advantages of bamboo, regulates the microstructure of the resulting carbon material, and significantly improves its charging capacity (308 mAh / g), plateau charging specific capacity (165 mAh / g), first charge-discharge efficiency (94.4%), and plateau capacity ratio (53.7%) in sodium-ion batteries, providing a new approach for the development of low-cost, high-performance sodium-ion battery anode materials.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] This invention provides a method for preparing bamboo-derived hard carbon materials, comprising the following steps:

[0012] The bamboo powder was initially sieved, and the fine bamboo powder after initial sieve was acid-washed once, washed with water until neutral, filtered and dried to obtain purified refined bamboo powder.

[0013] Under an inert atmosphere, the purified bamboo powder is subjected to a first carbonization, a second acid washing, and a second carbonization in sequence to obtain the moso bamboo-derived hard carbon material.

[0014] The temperature of the secondary carbonization is higher than that of the primary carbonization.

[0015] Furthermore, the temperature of the primary carbonization is 300-800℃, preferably 300-500℃. This stage not only involves the initial removal of volatiles, but more importantly, through moderate pyrolysis, opens nanoscale channels within the fiber bundles, exposing deeply encapsulated inorganic impurities. Utilizing the open channels formed by pre-carbonization, the acid solution can penetrate deep into the carbon matrix, thoroughly removing stubborn ash-forming components such as Si, K, and Ca, and introducing abundant micropores (precursors to closed pores) left by impurity removal. After acid washing, the mixture is washed with water until neutral and then dried. The hemicellulose is essentially cured at 200-300℃. After decomposition, cellulose undergoes violent pyrolysis at 300-380℃, producing a large amount of volatile gases (CO, CO2) and tar; lignin begins to decompose slowly (lignin has a wide pyrolysis temperature range, extending to above 800℃); the secondary carbonization temperature is 1400-1500℃. At this high temperature, the micropores introduced in the early stage undergo self-healing and rearrangement, transforming into "closed pores" that facilitate the storage of sodium ions; at the same time, the high temperature repairs the surface etching defects caused by acid washing, significantly reducing the specific surface area, thereby improving the first efficiency (first coulombic efficiency).

[0016] Furthermore, the bamboo powder is initially sieved using a 200-mesh sieve.

[0017] Furthermore, during the first pickling process: the acid used is hydrochloric acid, the concentration of the hydrochloric acid is 1 mol / L, and the pickling time is 12 h.

[0018] Furthermore, during the secondary pickling: the acid used is hydrochloric acid, the concentration of the hydrochloric acid is 1 mol / L, and the secondary pickling time is 6 h.

[0019] Furthermore, during the first carbonization process: the heating rate is 5°C / min, and the holding time is 120min.

[0020] Furthermore, during the secondary carbonization process: the heating rate is 5°C / min, and the holding time is 180min.

[0021] The present invention also provides a bamboo-derived hard carbon material prepared according to the above method.

[0022] The present invention also provides a sodium-ion battery, wherein the negative electrode is the aforementioned bamboo-derived hard carbon material.

[0023] The present invention also provides an application of the above-mentioned bamboo-derived hard carbon material in the preparation of sodium-ion batteries, wherein the bamboo-derived hard carbon material serves as the negative electrode of the sodium-ion battery.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] 1. High capacity: The bamboo-derived hard carbon material prepared by this invention maintains a high reversible specific capacity of over 308 mAh / g while achieving an initial coulombic efficiency of up to 94.4%. This is mainly attributed to the fact that pre-carbonization precisely exposes impurities without causing pore collapse, and the secondary carbonization perfectly repairs surface defects, significantly reducing irreversible sodium loss.

[0026] 2. Extremely high plateau capacity ratio (excellent energy density): The plateau capacity ratio of traditional biomass hard carbon is often less than 40%. The plateau charge specific capacity of the material of this invention is as high as 165mAh / g, accounting for 53.7% of the total capacity. This indicates that the material has formed an extremely perfect closed-cell structure, which greatly improves the battery's operating voltage plateau and overall energy density.

[0027] 3. Excellent microstructural stability: XRD and SEM characterization confirmed that this process, while preserving the natural vascular bundle conductive framework of moso bamboo, increased the interlayer spacing (d). 002 This enables rapid sodium ion transport dynamics. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 This invention provides a method for preparing bamboo-derived hard carbon materials and a flowchart for assembling sodium-ion half-cells using these materials.

[0030] Figure 2 SEM images of the bamboo-derived hard carbon materials prepared in Example 1 and Comparative Example 1 of the present invention, where (a) is Comparative Example 1 and (b) is Example 1;

[0031] Figure 3 The X-ray diffraction (XRD) patterns of the bamboo-derived hard carbon materials prepared in Example 1 and Comparative Example 1 of this invention;

[0032] Figure 4 The images show the Raman spectra of the bamboo-derived hard carbon materials prepared in Example 1 and Comparative Example 1 of this invention.

[0033] Figure 5 The charge-discharge curves are shown for sodium-ion button cells assembled using the bamboo-derived hard carbon materials prepared in Examples 1-4 and Comparative Examples 1-3 of this invention. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] An embodiment of the present invention provides a method for preparing a bamboo-derived hard carbon material, comprising the following steps:

[0040] Step 1: Hard carbon precursor pretreatment

[0041] The bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieving was washed with 1 mol / L hydrochloric acid for 12 hours. It was then thoroughly washed in deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder, which is the pretreated hard carbon precursor.

[0042] Step 2: Pre-carbonization process (i.e., primary carbonization process)

[0043] Purified bamboo powder was pre-carbonized under an inert atmosphere (preferably nitrogen) at a temperature of 300℃-800℃ (preferably 500℃), a heating rate of 5℃ / min, and a holding time of 120min. Afterward, it was cooled to room temperature to obtain bamboo powder activated carbon. The activated carbon was then acid-washed in 1mol / L hydrochloric acid for 6 hours, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder activated carbon. This stage not only involves preliminary removal of volatiles but, more importantly, opens nanoscale channels within the fiber bundles through moderate pyrolysis, exposing... The process exposes deep-seated inorganic impurities; utilizing the open channels formed by pre-carbonization, the acid solution can penetrate deep into the carbon matrix, thoroughly removing stubborn ash-forming components such as Si, K, and Ca, and introducing abundant micropores (the precursors to closed pores) left by impurity removal; after acid washing, the solution is washed with water until neutral and then dried; hemicellulose is basically decomposed at 200-300℃; cellulose undergoes violent pyrolysis at 300-380℃, producing a large amount of volatile gases (CO, CO2) and tar; lignin begins to decompose slowly (lignin has a wide pyrolysis temperature range, extending to above 800℃).

[0044] Step 3: Secondary carbonization process

[0045] Purified bamboo powder activated carbon is carbonized under an inert atmosphere (preferably nitrogen) at a temperature of 1400℃-1500℃ (preferably 1400℃), with a heating rate of 5℃ / min and a holding time of 180min. After cooling to room temperature, a bamboo-derived hard carbon material is obtained. At this high temperature, the micropores introduced in the early stage undergo self-healing and rearrangement, transforming into "closed pores" that facilitate the storage of sodium ions. At the same time, the high temperature repairs the surface etching defects caused by acid washing, significantly reducing the specific surface area and thus improving the first efficiency (first coulombic efficiency).

[0046] This invention uses bamboo powder as a precursor, first undergoing acid washing pretreatment, followed by low-temperature pre-carbonization at 300℃-800℃ (preferably 500℃) to construct a moderately open porous structure to remove deep impurities. After acid washing purification, high-temperature secondary carbonization is performed at 1400℃-1500℃ (preferably 1400℃) to induce micropore closure and surface repair. By strictly limiting the process flow of low-temperature pre-carbonization-acid washing to impurity removal-high-temperature reconstruction of closed pores, this invention successfully solves the contradiction of large specific surface area, low initial efficiency, and insufficient plateau capacity in biomass hard carbon materials. The bamboo-derived hard carbon material prepared by this invention has a unique low-defect, multi-closed-pore microstructure. When used as a sodium-ion battery anode, it exhibits high reversible specific capacity (>308mAh / g), excellent initial coulombic efficiency (>94%), and a high plateau capacity ratio (>53%), significantly improving the energy density and cycle stability of the entire battery, and providing a new approach for the development of low-cost, high-performance sodium-ion battery anode materials.

[0047] The choice of pre-carbonization temperature has a decisive influence on the evolution of the intermediate pore structure and the efficiency of subsequent acid washing for impurity removal.

[0048] 1. Limitations of the low-temperature range (e.g., 300℃): At 300℃, the organic components do not decompose completely. The resulting tar byproducts are prone to secondary condensation and clogging of the pores. Bamboo retains its original fibrous structure, causing inorganic impurities such as silicon and potassium to remain trapped deep within the incompletely decomposed organic matrix, making it difficult for acid to penetrate the material and limiting the efficiency of acid washing for impurity removal. As a result, the final material prepared in this way has high ash residue, reduced active sites, and unsatisfactory initial efficiency and capacity.

[0049] 2. Advantages of the preferred temperature (500℃) of this invention: At this temperature, cellulose and hemicellulose undergo complete pyrolysis, lignin begins to decompose, and the release of a large amount of small molecule gases constructs a rich network of mesoporous and macroporous structures. Unlike low-temperature pre-carbonization, the tar has essentially volatilized at this temperature, and the carbon skeleton has not yet undergone significant graphitization shrinkage. The material has high porosity, and this large number of open-pore structures significantly reduces the mass transfer resistance of acid penetration, ensuring the thorough removal of deep impurities. The rich open-pore structure formed at 500℃ provides the necessary spatial basis for the subsequent formation of closed pores at a high temperature of 1400℃.

[0050] 3. Limitations of the high-temperature zone (800℃): When the pre-carbonization temperature rises to 800℃, the carbon skeleton is prone to aromatization rearrangement, and graphite-like microcrystals begin to stack, leading to premature merging, shrinkage, or even closure of open pores. The carbon skeleton formed at 800℃ has high thermodynamic stability, making it difficult to form closed pores during subsequent secondary carbonization at 1400℃, thus limiting the number and volume of closed pores and resulting in a loss of sodium storage platform capacity.

[0051] The secondary carbonization temperature (1400-1500℃) of this invention is intended to achieve a precise balance between the disordered layer structure and the closed-cell volume, thereby solving the technical problems of low first-time efficiency and insufficient platform capacity of hard carbon in the prior art.

[0052] 1. Defects of the secondary carbonization temperature below the present invention: When the secondary carbonization temperature is below 1400℃ (such as 1000℃ or 1200℃), the carbon microcrystals are arranged randomly and are extremely small in size, and the material pores are mainly open pores.

[0053] Impact on first-efficiency: The open-pore structure results in an excessively large specific surface area, making it easy for the electrolyte to penetrate into the pores and continuously decompose to form an excessively thick SEI film, resulting in extremely high irreversible capacity.

[0054] Impact on capacity: Even when the temperature rises to 1200℃, although the micropores begin to shrink through the "bottleneck effect", the material cannot generate a significant low-voltage plateau capacity due to the lack of sufficient closed-pore volume to accommodate sodium metal clusters. The sodium storage mechanism is still mainly based on high-potential surface slope adsorption, resulting in low overall energy density.

[0055] 2. The technical effect of the preferred secondary carbonization temperature (1400℃) of the present invention: 1400℃ represents the optimal balance point for the evolution of the microstructure of hard carbon.

[0056] Microstructural features: Carbon microcrystals further grow and exhibit a typical disordered layer structure, with interlaced carbon layers forming numerous ultra-micro closed pores similar to those in a house of cards model. Simultaneously, high temperature treatment repairs surface defects, significantly reducing the specific surface area.

[0057] Performance Leap: This unique structure delivers a dual technological advantage: firstly, the extremely low specific surface area significantly reduces SEI film formation, achieving a high first-efficiency of 94.4%; secondly, sodium clusters fill abundant closed pores, contributing a substantial capacity (plateau capacity accounting for as much as 55.4%) at near-0V low potentials. Furthermore, the moderate interlayer spacing (approximately 0.37-0.38 nm) also accommodates the diffusion kinetics of sodium ions.

[0058] 3. Performance degradation above the secondary carbonization temperature of this invention: Once the temperature exceeds 1500℃, the carbon layer structure begins to evolve into a more thermodynamically stable graphite-like ordered stack. In pursuit of lower surface energy, the carbon layer framework supporting the closed pores softens and collapses, causing the closed pore volume to be compressed or even disappear. The reduction of closed pores directly leads to a significant drop in reversible capacity from 326mAh / g to 307mAh / g.

[0059] An embodiment of the present invention also provides a bamboo-derived hard carbon material prepared according to the above method.

[0060] An embodiment of the present invention also provides a sodium-ion battery, wherein the negative electrode is the aforementioned bamboo-derived hard carbon material.

[0061] Figure 1 The present invention relates to a bamboo-derived hard carbon material (corresponding to...) Figure 1 The invention discloses a method for preparing bamboo-derived hard carbon and a flowchart of assembling a sodium-ion half-cell using this bamboo-derived hard carbon material. The sodium-ion battery of this invention exhibits a discharge specific capacity of over 326 mAh / g, a charge specific capacity of over 308 mAh / g, high specific capacity, high energy density, an initial efficiency of over 94.4%, and a plateau charge specific capacity of 165 mAh / g accounting for 53.7% of the total, demonstrating excellent sodium storage performance.

[0062] In a preferred embodiment of the present invention, the assembly method of the sodium-ion battery is as follows: The above-mentioned bamboo-derived hard carbon material is used as the negative electrode active material. The negative electrode active material is mixed with binder PVDF (polyvinylidene fluoride) and conductive agent Super P in a mass ratio of 8:1:1. NMP (N-methylpyrrolidone) is added to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto an aluminum foil current collector and vacuum dried to form a circular electrode sheet with a diameter of 12 mm, which is used as the negative electrode sheet. A sodium metal sheet is used as the positive electrode sheet. The electrolyte composition is a 0.5 mol / L-1 mol / L NaFP6 diethylene glycol dimethyl ether solution. The sodium metal sheet, negative electrode sheet, and electrolyte are assembled into a sodium-ion half-cell in a glove box containing argon gas. A CR2032 specification battery casing is used. The assembled battery is sealed using a button cell sealing machine. After being removed from the glove box, it is left to stand at room temperature for 12 hours to obtain a sodium-ion button cell half-cell.

[0063] An embodiment of the present invention also provides an application of the above-mentioned bamboo-derived hard carbon material in the preparation of sodium-ion batteries, wherein the bamboo-derived hard carbon material serves as the negative electrode of the sodium-ion battery.

[0064] This invention first involves acid washing of bamboo powder to remove surface impurities and ash, followed by drying and pretreatment. The washed and dried bamboo powder is then pre-carbonized (i.e., primary carbonization) in an inert gas atmosphere at a specific temperature and heating rate. The pre-carbonized activated carbon material is then washed, filtered, and dried in a hydrochloric acid solution of a specific concentration. Subsequently, the treated activated carbon undergoes a high-temperature secondary carbonization in an inert gas atmosphere at a specific temperature and heating rate to obtain bamboo-derived hard carbon material. This bamboo-derived hard carbon material is mixed with a conductive agent (Super P) and a binder (PVDF), and then sequentially ground, homogenized, coated, dried, rolled, and sliced ​​to assemble a 2032 coin cell. By synergistically controlling the temperatures of the pre-carbonization and secondary carbonization processes, a bamboo-derived hard carbon material that balances high capacity and high initial efficiency is prepared.

[0065] In the following embodiments and comparative examples of the present invention, the performance testing methods are as follows:

[0066] 1. SEM testing: Tested using a German ZEISS Sigma 360.

[0067] 2. Charge and discharge performance test: Electrochemical performance was tested using the WIHW-200-160CH battery testing system at 25℃, 0-3.0V operating voltage, and 0.1C current density.

[0068] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0069] All raw materials used in the embodiments of the present invention were obtained through commercial purchase.

[0070] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0071] The technical solution of the present invention will be further illustrated by the following embodiments.

[0072] Example 1

[0073] A method for preparing a bamboo-derived hard carbon material (pre-carbonization at 500℃, secondary carbonization at 1400℃), the steps are as follows:

[0074] Step 1: Hard carbon precursor pretreatment

[0075] Bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieving was then washed with 1 mol / L hydrochloric acid for 12 hours. The powder was then thoroughly washed in deionized water until neutral, filtered, and dried at 100°C to obtain purified bamboo powder.

[0076] Step 2: Pre-carbonization process

[0077] The purified bamboo powder was carbonized under an inert atmosphere (nitrogen, the same below) at a temperature of 500℃, a heating rate of 5℃ / min, and a holding time of 120min. After cooling to room temperature, bamboo powder activated carbon was obtained. The bamboo powder activated carbon was acid-washed in 1mol / L hydrochloric acid for 6h, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder activated carbon.

[0078] Step 3: Secondary carbonization process

[0079] The purified bamboo powder activated carbon was subjected to secondary carbonization under an inert atmosphere. The secondary carbonization temperature was 1400℃, the heating rate was 5℃ / min, and the holding time was 180min. After cooling to room temperature, the bamboo-derived hard carbon material was obtained.

[0080] The above-mentioned bamboo-derived hard carbon materials were assembled into batteries and their performance was tested. The specific process is as follows:

[0081] The above-mentioned bamboo-derived hard carbon material was used as the negative electrode active material. The negative electrode active material was mixed with binder PVDF (polyvinylidene fluoride) and conductive agent Super P in a mass ratio of 8:1:1. 0.6 mL of NMP (N-methylpyrrolidone) was added to prepare the negative electrode slurry. The negative electrode slurry was uniformly coated on an aluminum foil current collector and vacuum dried to form a circular electrode sheet with a diameter of 12 mm, which was used as the negative electrode sheet. Sodium metal sheet was used as the positive electrode sheet. The electrolyte composition was a 1 mol / L NaFP6 diethylene glycol dimethyl ether solution. The sodium metal sheet, negative electrode sheet and electrolyte were assembled into a sodium-ion half-cell in an argon-filled glove box. A CR2032 specification battery casing was used. The assembled battery was sealed using a button cell sealing machine. After being removed from the glove box, it was left to stand at room temperature for 12 hours to obtain a sodium-ion button cell half-cell. Electrochemical performance was tested using the WIHW-200-160CH battery testing system at 25℃, 0-3.0V operating voltage, and 0.1C current density.

[0082] Example 2

[0083] A method for preparing a bamboo-derived hard carbon material (pre-carbonization at 300℃, secondary carbonization at 1400℃), the steps are as follows:

[0084] Step 1: Hard carbon precursor pretreatment

[0085] Bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieving was then washed with 1 mol / L hydrochloric acid for 12 hours. The powder was then thoroughly washed in deionized water until neutral, filtered, and dried at 100°C to obtain purified bamboo powder.

[0086] Step 2: Pre-carbonization process

[0087] The purified bamboo powder was carbonized under an inert atmosphere at a temperature of 300℃, a heating rate of 5℃ / min, and a holding time of 120min. After cooling to room temperature, bamboo powder activated carbon was obtained. The bamboo powder activated carbon was acid-washed in 1mol / L hydrochloric acid for 6h, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder activated carbon.

[0088] Step 3: Secondary carbonization process

[0089] The purified bamboo powder activated carbon was subjected to secondary carbonization under an inert atmosphere. The secondary carbonization temperature was 1400℃, the heating rate was 5℃ / min, and the holding time was 180min. After cooling to room temperature, the bamboo-derived hard carbon material was obtained.

[0090] The above-mentioned bamboo-derived hard carbon materials were assembled into batteries and their performance was tested. The specific process was the same as in Example 1.

[0091] Example 3

[0092] A method for preparing a bamboo-derived hard carbon material (pre-carbonization at 500℃, secondary carbonization at 1500℃), the steps are as follows:

[0093] Step 1: Hard carbon precursor pretreatment

[0094] Bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieving was then washed with 1 mol / L hydrochloric acid for 12 hours. The powder was then thoroughly washed in deionized water until neutral, filtered, and dried at 100°C to obtain purified bamboo powder.

[0095] Step 2: Pre-carbonization process

[0096] Purified bamboo powder was carbonized under an inert atmosphere at a temperature of 500℃, a heating rate of 5℃ / min, and a holding time of 120min. After cooling to room temperature, bamboo powder activated carbon was obtained. The bamboo powder activated carbon was then acid-washed in 1mol / L hydrochloric acid for 6h, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder activated carbon.

[0097] Step 3: Secondary carbonization process

[0098] The purified bamboo powder activated carbon was subjected to secondary carbonization under an inert atmosphere. The secondary carbonization temperature was 1500℃, the heating rate was 5℃ / min, and the holding time was 180min. After cooling to room temperature, the bamboo-derived hard carbon material was obtained.

[0099] The above-mentioned bamboo-derived hard carbon materials were assembled into batteries and their performance was tested. The specific process was the same as in Example 1.

[0100] Example 4

[0101] A method for preparing a bamboo-derived hard carbon material (pre-carbonization at 800℃, secondary carbonization at 1400℃), the steps are as follows:

[0102] Step 1: Hard carbon precursor pretreatment

[0103] Bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieving was then washed with 1 mol / L hydrochloric acid for 12 hours. The powder was then thoroughly washed in deionized water until neutral, filtered, and dried at 100°C to obtain purified bamboo powder.

[0104] Step 2: Pre-carbonization process

[0105] Purified bamboo powder was carbonized under an inert atmosphere at a temperature of 800℃, a heating rate of 5℃ / min, and a holding time of 120min. After cooling to room temperature, bamboo powder activated carbon was obtained. The bamboo powder activated carbon was then acid-washed in 1mol / L hydrochloric acid for 6h, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder activated carbon.

[0106] Step 3: Secondary carbonization process

[0107] The purified bamboo powder activated carbon was subjected to secondary carbonization under an inert atmosphere. The secondary carbonization temperature was 1400℃, the heating rate was 5℃ / min, and the holding time was 180min. After cooling to room temperature, the bamboo-derived hard carbon material was obtained.

[0108] The above-mentioned bamboo-derived hard carbon materials were assembled into batteries and their performance was tested. The specific process was the same as in Example 1.

[0109] Comparative Example 1: One-step carbonization at 1400℃ to prepare bamboo-derived hard carbon materials

[0110] Step 1: Hard carbon precursor pretreatment

[0111] Bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieving was then washed with 1 mol / L hydrochloric acid for 12 hours. The powder was then thoroughly washed in deionized water until neutral, filtered, and dried at 100°C to obtain purified bamboo powder.

[0112] Step 2: Carbonization process

[0113] Purified bamboo powder was carbonized under an inert atmosphere at a temperature of 1400℃, a heating rate of 5℃ / min, and a holding time of 180min. After cooling to room temperature, bamboo-derived hard carbon material was obtained. The bamboo powder hard carbon was acid-washed in 1mol / L hydrochloric acid for 6h, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain bamboo-derived hard carbon material.

[0114] The above-mentioned bamboo-derived hard carbon materials were assembled into batteries and their performance was tested. The specific process was the same as in Example 1.

[0115] Compare with Example 2

[0116] A method for preparing a bamboo-derived hard carbon material (pre-carbonization at 500℃, secondary carbonization at 1000℃), the steps are as follows:

[0117] Step 1: Hard carbon precursor pretreatment

[0118] Bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieve was washed with 1 mol / L hydrochloric acid for 12 hours. It was then thoroughly washed in deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder, which is the pretreated hard carbon precursor.

[0119] Step 2: Pre-carbonization process

[0120] The purified bamboo powder was carbonized under an inert atmosphere at a temperature of 500℃, a heating rate of 5℃ / min, and a holding time of 120min. After cooling to room temperature, bamboo powder activated carbon was obtained. The bamboo powder activated carbon was acid-washed in 1mol / L hydrochloric acid for 6h, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder activated carbon.

[0121] Step 3: Secondary carbonization process

[0122] The purified bamboo powder activated carbon was subjected to secondary carbonization under an inert atmosphere. The secondary carbonization temperature was 1000℃, the heating rate was 5℃ / min, and the holding time was 180min. After cooling to room temperature, the bamboo-derived hard carbon material was obtained.

[0123] The above-mentioned bamboo-derived hard carbon materials were assembled into batteries and their performance was tested. The specific process was the same as in Example 1.

[0124] Compare with Example 3

[0125] A method for preparing a bamboo-derived hard carbon material (pre-carbonization at 500℃, secondary carbonization at 1200℃), the steps are as follows:

[0126] Step 1: Hard carbon precursor pretreatment

[0127] Bamboo powder was initially sieved using a 200-mesh sieve. The fine bamboo powder after initial sieving was then washed with 1 mol / L hydrochloric acid for 12 hours. The powder was then thoroughly washed in deionized water until neutral, filtered, and dried at 100°C to obtain purified bamboo powder.

[0128] Step 2: Pre-carbonization process

[0129] The purified bamboo powder was carbonized under an inert atmosphere at a temperature of 500℃, a heating rate of 5℃ / min, and a holding time of 120min. After cooling to room temperature, bamboo powder activated carbon was obtained. The bamboo powder activated carbon was acid-washed in 1mol / L hydrochloric acid for 6h, washed with deionized water until neutral, filtered, and dried at 100℃ to obtain purified bamboo powder activated carbon.

[0130] Step 3: Secondary carbonization process

[0131] The purified bamboo powder activated carbon was subjected to secondary carbonization under an inert atmosphere. The secondary carbonization temperature was 1200℃, the heating rate was 5℃ / min, and the holding time was 180min. After cooling to room temperature, the bamboo-derived hard carbon material was obtained.

[0132] The above-mentioned bamboo-derived hard carbon materials were assembled into batteries and their performance was tested. The specific process was the same as in Example 1.

[0133] Figure 2The images show SEM images of the bamboo-derived hard carbon materials prepared in Example 1 and Comparative Example 1 of this invention, where (a) is Comparative Example 1 and (b) is Example 1. It can be seen that:

[0134] The hard carbon material prepared by Comparative Example 1 (one-step carbonization) has a relatively rough surface with numerous granular protrusions or surface defects. Furthermore, due to the lack of low-temperature pre-carbonization and acid washing for opening pores, some impurities and irregular structures are directly solidified on the carbon layer surface. In contrast, the hard carbon material prepared by Example 1 of this invention (two-step carbonization) exhibits a smooth, dense, and clean surface morphology, with the vascular bundle structure remaining intact and no obvious openings or surface impurities remaining. This indicates that after pre-carbonization and acid washing at 500℃ to remove impurities, followed by a secondary carbonization at 1400℃, surface defects are effectively repaired, the specific surface area is significantly reduced, and side reactions of the electrolyte on the material surface are reduced, thereby achieving a higher initial coulombic efficiency.

[0135] Figure 3 The X-ray diffraction patterns of the bamboo-derived hard carbon materials prepared in Example 1 and Comparative Example 1 of this invention show that both samples exhibit two broad and blunt diffraction peaks at 2θ angles of approximately 24° and 43°, respectively, corresponding to the (002) and (100) crystal planes of the disordered layered carbon structure, indicating that both possess typical amorphous hard carbon structures. Compared to Comparative Example 1, the (002) diffraction peak of Example 1 is slightly shifted to a lower angle. According to Bragg's equation, a smaller angle implies a smaller interlayer spacing (d). 002 The larger the value, the better. This indicates that the "low-temperature pre-carbonization-acid washing-high-temperature reconstruction" process used in this invention effectively expands the interlayer spacing of carbon microcrystals. The expanded interlayer spacing lowers the energy barrier for sodium ions to insert and extract between carbon layers, thereby endowing the material with superior rate performance and kinetic characteristics.

[0136] Figure 4 The Raman spectra of the bamboo-derived hard carbon materials prepared in Example 1 and Comparative Example 1 of this invention show that:

[0137] The samples of Example 1 and Control Example 1 were both at 1350 cm. -1 Nearby (D peak) and 1580 cm -1 Near the G peak, two distinct characteristic peaks are observed. The D peak corresponds to defects and disorder vibrations in the carbon lattice, while the G peak corresponds to sp... 2 In-plane stretching vibrations of hybrid carbon atoms.

[0138] Compared with Control Example 1, Example 1 I D / I GThe (defect strength / graphitization strength) ratio may be slightly increased, indicating that the internal carbon microcrystals still maintain a highly disordered layered structure. This highly disordered structure is consistent with the XRD test results, confirming that the "house of cards" model formed by the two-step carbonization method in Example 1 can effectively suppress excessive graphitization stacking of carbon layers, providing abundant defect sites and closed-pore spaces for sodium ion storage. In contrast, due to the lack of removal of impurities in Control Example 1, impurities may have catalyzed graphitization at high temperatures, leading to an increase in local order, which is not conducive to sodium storage. The charge-discharge curves of sodium-ion coin cells assembled using the bamboo-derived hard carbon materials prepared in Examples 1-4 and Control Examples 1-3 of this invention are shown below. Figure 5 As shown, the sodium-ion coin cell assembled using the bamboo-derived hard carbon material prepared in Comparative Example 1 has a specific charge capacity of 213 mAh / g, a plateau specific charge capacity of 133 mAh / g (62%), and an initial coulombic efficiency of 53%. The sodium-ion coin cell assembled using the bamboo-derived hard carbon material prepared in Comparative Example 2 has a specific charge capacity of 185 mAh / g, with no obvious plateau sodium storage phenomenon, and an initial coulombic efficiency of 42%. The sodium-ion coin cell assembled using the bamboo-derived hard carbon material prepared in Comparative Example 3 has a specific charge capacity of over 235 mAh / g, a plateau specific charge capacity of 92 mAh / g, and an initial coulombic efficiency of 47%. The sodium-ion coin cell assembled using the bamboo-derived hard carbon material prepared in Example 1 has a specific charge capacity of over 308 mAh / g, with a plateau specific charge capacity of 165 mAh / g accounting for 53% and an initial coulombic efficiency of 94%. The sodium-ion coin cell assembled using the bamboo-derived hard carbon material prepared in Example 2 has a specific charge capacity of over 282 mAh / g, with a plateau specific charge capacity of 156 mAh / g accounting for 55% and an initial coulombic efficiency of 64%. The sodium-ion coin cell assembled using the bamboo-derived hard carbon material prepared in Example 3 has a specific charge capacity of over 282 mAh / g, with a plateau specific charge capacity of 165 mAh / g accounting for 59% and an initial coulombic efficiency of 72%. The sodium-ion coin cell assembled using the bamboo-derived hard carbon material prepared in Example 4 has a specific charge capacity of over 285 mAh / g, with a plateau specific charge capacity of 159 mAh / g accounting for 56% and an initial coulombic efficiency of 59%.

[0139] from Figure 5The data shows that in the preparation of hard carbon materials, by controlling the temperature and carbonization method of the precursor pre-carbonization and secondary carbonization processes in Examples 1-4 and Comparative Examples 1-3 of the present invention, bamboo powder-derived hard carbon materials can be obtained for preparing hard carbon negative electrode sheets and assembling 2032 coin cells. Among them, the sodium-ion battery assembled using the bamboo-derived hard carbon material prepared in Example 1 has the best electrochemical performance, with a discharge specific capacity of over 326 mAh / g and a charge specific capacity of over 308 mAh / g. The specific capacity is high, which is beneficial to improving the energy density of the battery. The first efficiency reaches over 94%, and the plateau charge specific capacity reaches 165 mAh / g, accounting for 53%.

[0140] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material derived from Phyllostachys edulis, characterized by, The method comprises the following steps: The bamboo powder is subjected to primary screening, and the screened bamboo powder is subjected to acid washing, water washing, filtering and drying to obtain purified bamboo powder; The purified bamboo powder is subjected to carbonization, secondary acid washing and secondary carbonization in an inert atmosphere to obtain the bamboo-derived hard carbon material. The temperature of the secondary carbonization is higher than that of the primary carbonization.

2. The process for the production of bamboo derived hard carbon material as claimed in claim 1 wherein, The temperature of the primary carbonization is 300-800℃, and the temperature of the secondary carbonization is 1400-1500℃.

3. The process for the preparation of bamboo derived hard carbon material as claimed in claim 1 wherein, The bamboo powder is subjected to primary screening with a 200-mesh screen.

4. The method for preparing bamboo-derived hard carbon material according to claim 1, characterized in that, During the primary acid washing, hydrochloric acid is used, the concentration of the hydrochloric acid is 1 mol / L, and the time of the primary acid washing is 12 h.

5. The method for preparing bamboo-derived hard carbon material according to claim 1, characterized in that, During the secondary acid washing, hydrochloric acid is used, the concentration of the hydrochloric acid is 1 mol / L, and the time of the secondary acid washing is 6 h.

6. The method for preparing bamboo-derived hard carbon material according to claim 1, characterized in that, During the primary carbonization, the heating rate is 5℃ / min, and the holding time is 120 min.

7. The method for preparing bamboo-derived hard carbon material according to claim 1, characterized in that, During the secondary carbonization, the heating rate is 5℃ / min, and the holding time is 120 min.

8. A bamboo-derived hard carbon material, characterized in that, The bamboo-derived hard carbon material is prepared by the method according to any one of claims 1-7.

9. A sodium-ion battery, characterized in that, The negative electrode is the bamboo-derived hard carbon material according to claim 8.

10. Use of the bamboo-derived hard carbon material as claimed in claim 8 in the preparation of a sodium-ion battery, characterized in that, The bamboo-derived hard carbon material is used as a negative electrode of a sodium ion battery.

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