Plasma ball-milling bamboo-based hard carbon negative electrode material and preparation method and application thereof

Abstract

This invention discloses a bamboo-based hard carbon anode material prepared by plasma ball milling, its preparation method, and its application. The process involves pretreatment, pre-oxidation, plasma ball milling, and high-temperature carbonization. The naturally occurring regular hierarchical channels and abundant cellulose content of southern moso bamboo provide an ideal structural template for hard carbon preparation. Through the synergistic effect of pre-oxidation and plasma ball milling, pre-oxidation introduces oxygen-containing functional groups to guide the orderly stacking of carbon layers, while plasma ball milling removes ash and optimizes the conductivity of the carbon skeleton through mechanochemical effects. The anode prepared from the sample milled for 15 min exhibits conductivity at 1.0 A·g⁻¹. ‑1 After 150 cycles at a current density, it still maintains 254.9 mAh·g. ‑1 It has a reversible specific capacity and a capacity retention rate of up to 88%. Thanks to the structural regulation strategy, the bamboo-based hard carbon anode material after plasma ball milling has shown excellent sodium storage performance as a sodium-ion battery anode.

Description

Technical Field

[0001] This invention relates to the field of electrode material technology, and in particular to the construction of a bamboo-based hard carbon anode material by plasma ball milling, its preparation method and application. Background Technology

[0002] Sodium-ion batteries (SIBs) are considered an important complement to lithium-ion batteries due to their high safety, abundant raw materials, and good low-temperature performance, and have broad prospects in large-scale energy storage. However, sodium ions have a relatively large radius (Na... + 1.02 Å vs. Li + The low sodium density (0.76 Å) of graphite leads to slow diffusion kinetics in electrode materials, and the extremely low sodium storage capacity of commercial graphite anodes severely restricts the practical application of SIBs. Therefore, developing low-cost anode materials that combine high capacity with good kinetic performance has become crucial for promoting the industrialization of sodium-ion batteries.

[0003] Hard carbon materials, with their large interlayer spacing and abundant disordered structure, exhibit ideal sodium storage potential and cost advantages, making them one of the most promising sodium-ion battery anode materials. However, low intrinsic conductivity, poor rate performance, and poor long-cycle stability limit their further application. To improve the electrochemical performance of hard carbon, researchers have explored various strategies, including precursor structure regulation, composite material construction, and heteroatom doping. Among these, heteroatom doping has been proven to effectively enhance material conductivity, expand carbon interlayer spacing, and thus promote sodium storage. + The insertion and extraction of phosphorus. For example, phosphorus-doped hard carbon microspheres (PHCS) were prepared by introducing a phosphorus source with phytic acid, at 0.1 A g. - ¹Achieve 293.5 mAh g - ¹Reversible capacity, and at 5 Ag - ¹ Stable cycling for over 2000 cycles; Nitrogen / sulfur co-doped hard carbon synthesized using benzoxazine resin exhibits excellent rate performance and stability for up to 2000 cycles.

[0004] However, most existing doping methods rely on complex chemical processes or expensive precursors, resulting in cumbersome processes, high costs, and hindering large-scale preparation. This invention proposes a method for preparing bamboo-based hard carbon materials based on plasma ball milling technology. Using southern moso bamboo as raw material, this method achieves precise control over the microstructure of hard carbon materials through the synergistic treatment of pre-oxidation and plasma ball milling, without relying on complex chemical modifications. The pre-oxidation process constructs a stable carbon layer framework and introduces abundant active sites, while plasma ball milling further optimizes the carbon layer arrangement, increases defect concentration, and expands interlayer spacing through efficient mechanochemical action. This combination not only simplifies traditional doping processes but also effectively improves the conductivity and sodium ion diffusion rate of the material. The resulting hard carbon anode exhibits excellent rate performance and cycle stability in sodium-ion batteries, providing a new path for the green preparation and industrial application of low-cost, high-performance hard carbon materials. Summary of the Invention

[0005] This disclosure provides a bamboo-based hard carbon anode material based on plasma ball milling, its preparation method, and its application, which can effectively solve the above-mentioned problems.

[0006] This disclosure is implemented as follows:

[0007] This first aspect discloses a method for preparing a bamboo-based hard carbon anode material by plasma ball milling, comprising the following steps:

[0008] Bamboo charcoal precursors were obtained by using 3-5 year old southern moso bamboo as the sole carbon source through hydrochloric acid pretreatment and muffle furnace pre-oxidation. This specific bamboo species possesses moderate vascular bundle density, high cellulose content, and low inorganic impurities. The pretreated middle section of the bamboo culm provides a homogeneous and consistently reactive precursor base for subsequent pre-oxidation and plasma ball milling. This strict limitation on raw materials ensures the reproducibility and superiority of the resulting bamboo-based hard carbon materials in terms of microstructure (e.g., interlayer spacing, defect concentration) and electrochemical performance.

[0009] The naturally regular multi-level channels and rich cellulose components of moso bamboo in southern China provide an ideal structural template for the preparation of hard carbon.

[0010] The pre-oxidized bamboo charcoal precursor was placed in a plasma ball mill and subjected to mechanochemical activation under the protection of an argon-hydrogen mixed gas (argon:hydrogen = 95:5, volume ratio). Specific process parameters were: ball-to-material ratio 10:1-20:1, rotation speed 200-300 r / min, with four gradient treatment times set for 5 min, 15 min, 30 min, and 1 h. The ball-milled precursors all exhibited a uniform powder with no obvious particles.

[0011] The precursor, after ball milling, was subjected to high-temperature carbonization under an argon-hydrogen atmosphere to finally obtain the high-performance bamboo-based hard carbon material.

[0012] A method for preparing a bamboo-based hard carbon anode material by plasma ball milling includes the following steps:

[0013] 1) Raw material pretreatment: Cut natural bamboo into small pieces, use dilute hydrochloric acid to acid wash to remove inorganic ash inside and on the surface of the bamboo, then use deionized water and anhydrous ethanol alternately for ultrasonic cleaning, and dry at 60-80℃ to obtain clean bamboo precursor.

[0014] 2) Pre-oxidation treatment: The bamboo precursor is heated to 250-350℃ in air at a heating rate of 2℃ / min and held for 1.5-2 h to obtain pre-oxidized bamboo powder with an oxygen content of 5-15 at.%, which exists in the form of covalent bonds.

[0015] 3) Plasma ball milling: Pre-oxidized bamboo powder is subjected to planetary plasma ball milling for 5 to 30 minutes under a protective atmosphere, a ball-to-powder mass ratio of 10:1-20:1, and a rotation speed of 300-500 rpm, and the particle size is controlled between 0.5 µm and 2 µm.

[0016] 4) High-temperature carbonization: The ball-milled powder is heated to 1000-1300℃ at a heating rate of 5℃ / min and held for 1-3 h under an argon protective atmosphere to obtain bamboo-based hard carbon anode material.

[0017] In some implementations, in step 3), an intermittent ball milling mode is used, running for 5-10 minutes and pausing for 5-10 minutes.

[0018] In some embodiments, in step 4), the final temperature of the high-temperature carbonization is 1200°C, and the holding time is 3 hours.

[0019] In some embodiments, the protective atmosphere for ball milling is argon, an argon-hydrogen mixture, hydrogen, or nitrogen.

[0020] In some embodiments, the natural bamboo is Fujian southern moso bamboo, which has a growth cycle of 3-5 years.

[0021] In some embodiments, the specific surface area of ​​the bamboo-based hard carbon anode material is controlled at 5–30 m² / g; the hard carbon interlayer spacing of the bamboo-based hard carbon anode material is controlled at 0.36–0.40 nm.

[0022] This second aspect discloses a bamboo-based hard carbon anode material prepared by plasma ball milling, wherein the bamboo-based hard carbon anode material is obtained by the above preparation method.

[0023] This third aspect discloses the application of a plasma-milled bamboo-based hard carbon anode material, and the application of the bamboo-based hard carbon material prepared by the above method or the above-mentioned bamboo-based hard carbon anode material in the anode of a sodium-ion battery.

[0024] The beneficial effects of this invention are:

[0025] (1) This invention provides a simple, low-cost, and easily industrialized path for optimizing the performance of hard carbon by pre-treating bamboo hard carbon precursors with controllable ball milling time. This method effectively optimizes the particle size, specific surface area, and defect structure of hard carbon products through plasma ball milling rather than complex chemical modification, thereby synergistically improving its ion diffusion rate and charge transfer kinetics when used as a negative electrode in sodium-ion batteries, exhibiting excellent rate performance and cycle life.

[0026] (2) The high-performance hard carbon material prepared by the method of this invention exhibits excellent electrochemical performance when applied to the anode of a sodium-ion battery. For example, at 0.2 A g... - ¹ After 50 cycles at high current density, it still maintains 303.8 mAhg. - ¹High reversible specific capacity; at 1 A g - ¹At extremely high rates, it can release 254.9 mAh g⁻¹ - ¹High specific capacity. This demonstrates that by controlling the ball milling time—a simple process—the specific capacity of Na in hard carbon materials can be significantly increased. + Its storage capacity and high-rate performance enable it to maintain a high capacity retention rate even during long-term cycles. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 These are XRD patterns of the hard carbon from Comparative Examples 1 and 2, and the hard carbon from Examples 1, 2, and 3 of this application.

[0029] Figure 2 These are SEM images of the hard carbon from Comparative Examples 1 and 2, and Examples 1, 2, and 3 of this application.

[0030] Figure 3 These are nitrogen adsorption-desorption curves and pore size distribution diagrams of the hard carbon in Comparative Example 1 and Examples 1, 2, and 3 of this application.

[0031] Figure 4 These are the rate performance curves of the hard carbon materials of Comparative Examples 1 and 2 and Examples 1, 2, and 3 of this application.

[0032] Figure 5 The hard carbon samples from Comparative Examples 1 and 2, and Examples 1, 2, and 3 of this application, were tested at a current density of 0.2 A·g. -1 The cyclic performance curve is shown after 50 cycles under the given conditions.

[0033] Figure 6 The hard carbon samples of Comparative Examples 1 and 2, and Examples 1, 2, and 3 of this application, were subjected to a current density of 1 A·g. -1 The cyclic performance curve is shown after 150 cycles under certain conditions.

[0034] Figure 7 This is a flowchart illustrating the preparation process of bamboo-based hard carbon anode material controlled by plasma ball milling. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0037] This invention provides a method for preparing a bamboo-based hard carbon anode material by plasma ball milling, comprising the following steps:

[0038] S1. Raw material pretreatment: Natural bamboo is cut into small pieces and acid-washed with dilute hydrochloric acid to remove inorganic ash from the inside and surface of the bamboo. After ultrasonic cleaning with alternating deionized water and anhydrous ethanol, it is dried at 60-80℃ to obtain a clean bamboo precursor. Inorganic ash includes salts such as K, Ca, and Mg.

[0039] S2. Pre-oxidation treatment: The bamboo precursor is heated to 250-350℃ in air at a heating rate of 2℃ / min and held for 1.5-2 h to obtain pre-oxidized bamboo powder with an oxygen content of 5-15 at.%, which exists in a covalent bond form.

[0040] Oxidation temperature and time are crucial in determining material yield and final structure: If the pre-oxidation temperature is too low (<250℃) or the time is too short (<1.5 h), the pyrolysis of cellulose within the bamboo is insufficient, failing to form a sufficiently thermally stable cross-linked structure. This leads to the release of a large amount of volatile components during subsequent high-temperature carbonization, significantly reducing the carbonization yield and making it difficult to form a stable hard carbon skeleton. Conversely, if the pre-oxidation temperature is too high (>350℃) or the time is too long (>3 h), the bamboo will undergo excessive oxidation or even combustion, resulting in a significant loss of carbon source. This also leads to a sharp decrease in carbonization yield, and the formed carbon structure is too dense, hindering the insertion and transport of sodium ions. Therefore, precisely controlling the pre-oxidation conditions at 300℃ and 2 h is the optimal balance point for achieving high carbonization yield and an ideal porous hard carbon structure.

[0041] S3. Plasma ball milling: Pre-oxidized bamboo powder is subjected to planetary plasma ball milling for 5 to 30 minutes under a protective atmosphere, a ball-to-powder mass ratio of 10:1-20:1, and a rotation speed of 300-500 rpm, and the particle size is controlled between 0.5 µm and 2 µm.

[0042] The ball-to-particle ratio and rotational speed are key parameters affecting ball milling efficiency. A low ball-to-particle ratio (<10:1) results in insufficient grinding media, inadequate mechanochemical interaction, and limited material structure optimization. A high ball-to-particle ratio (>20:1) leads to excessive impact energy, potentially causing over-crushing and amorphization of the carbon skeleton, thus compromising its intrinsic structural advantages. Simultaneously, a low rotational speed (<300 rpm) fails to provide sufficient kinetic energy for effective plasma activation and mechanical exfoliation; a high rotational speed (>500 rpm) causes overheating of the reaction system and may induce powder agglomeration, which is also detrimental to obtaining uniform and ideal nanostructures. Therefore, precisely controlling the ball-to-particle ratio and rotational speed within the aforementioned optimal ranges is crucial for achieving efficient and controllable structural reconstruction of bamboo-based precursors.

[0043] S4. High-temperature carbonization: The ball-milled powder is heated to 1000-1300℃ at a heating rate of 5℃ / min under an argon protective atmosphere and held at that temperature for 1-3 h.

[0044] If the temperature is too low (<1000℃), the precursor carbonization will be incomplete, resulting in insufficient graphitization and poor conductivity with few sodium-storing active sites. If the temperature is too high (>1300℃), the carbon layer will become overly ordered, the pore structure will collapse, and the specific surface area will decrease sharply, which will weaken the sodium storage capacity and ion diffusion kinetics of the material. Therefore, precisely controlling the carbonization temperature within the range of 1000-1300℃ is the optimal condition for achieving high-capacity and high-stability bamboo-based hard carbon materials.

[0045] By precisely controlling the ball milling time, the particle size and structural defects of hard carbon precursors can be synergistically regulated. If the ball milling time is too short (<5 min), the mechanochemical activation is insufficient, making it difficult to effectively optimize the carbon layer structure and introduce enough defects; while if the ball milling time is too long (>30 min), it easily leads to excessive particle crushing and severe damage to the carbon layer structure, which is detrimental to the formation of a stable sodium storage structure. Therefore, controlling the ball milling time within 5-30 minutes is key to optimizing the material's microstructure and improving its electrochemical performance.

[0046] If the ball milling time is too short (e.g., less than 5 minutes), the effect on particle refinement and defect introduction of the precursor will be insignificant, and the improvement on the final electrochemical performance will be minimal. If the ball milling time is too long (e.g., more than 1 hour), the amorphous carbon structure in the precursor may be excessively destroyed, making it difficult to effectively form stable defects and closed-pore structures that are conducive to sodium storage during the subsequent carbonization process. At the same time, excessively refined particles may be detrimental to the process performance of electrode coating.

[0047] In step S3, an intermittent ball milling mode is adopted, i.e., "run for 5-10 minutes, pause for 5-10 minutes". The purpose is to effectively avoid localized overheating caused by the continuous accumulation of mechanical energy during the ball milling process. Localized overheating may cause unintended oxidation or structural changes in the precursor material, thereby affecting the uniformity and electrochemical performance of the final carbonized product. This intermittent mode ensures that the ball milling process is carried out within a controllable temperature range, allowing mechanical energy to act more effectively on particle refinement and defect introduction.

[0048] In step S4, the final temperature of the high-temperature carbonization is set to 1200°C, and the holding time is 3 hours. These high-temperature heat treatment parameters are crucial for forming the typical hard carbon structure.

[0049] At this high temperature, non-carbon elements in the precursor are effectively removed, and carbon atoms rearrange to form a highly disordered graphite-like microcrystalline structure, generating a large number of nanopores that are crucial for sodium storage. The structural defects introduced by ball milling in step S3 are partially retained and fixed in this process, ultimately constructing a hard carbon anode material with high specific capacity and excellent ion diffusion capability.

[0050] The natural bamboo mentioned is Fujian moso bamboo, which has a growth cycle of 3-5 years. Fujian moso bamboo is characterized by its thick culms and robust walls, resulting in a high yield. Its high fiber density exhibits excellent hardness, toughness, and compressive and bending strength, making it an ideal material for engineering structures.

[0051] Fujian moso bamboo, with its moderate vascular bundle density, high cellulose content, and low inorganic impurities, is selected for its central culm after pretreatment. The vascular bundle density of Fujian moso bamboo is approximately 4–6 bundles / mm², ensuring a uniform and stable fiber skeleton; the high cellulose content (>40%) guarantees the product's mechanical strength and thermal stability; and the low ash content (<1.5%) reduces processing losses. Pretreatment of the central culm primarily involves removing bamboo nodes. This is because bamboo nodes are areas of uneven structure and stress concentration in bamboo, where fiber direction is broken and lignin and silica content are high, severely affecting the uniformity of subsequent processing, product mechanical properties, and surface quality.

[0052] In the preparation of hard carbon anode materials, the final particle size after plasma ball milling is crucial. Optimal size is controlled to approximately 1 µm: excessively large sizes (>2 µm) indicate insufficient activation, resulting in low specific surface area and defect concentration, which is detrimental to sodium storage; excessively small sizes (<0.5 µm) will disrupt the carbon layer structure, leading to agglomeration and reducing tap density and interfacial stability. Precisely controlling the particle size to around 1 µm allows for sufficient structural activation while maintaining the integrity of the carbon framework and the continuity of the conductive network, thereby achieving excellent sodium storage capacity and cycle life.

[0053] The specific surface area of ​​hard carbon anode materials is controlled between 5 and 30 m² / g. Too low a surface area (<5 m² / g) leads to insufficient active sites and poor electrolyte wetting, affecting capacity and rate performance; too high a surface area (>30 m² / g) exacerbates side reactions, reducing first-efficiency performance and cycle stability. Optimizing this parameter can suppress side reactions while ensuring sodium storage sites, achieving a performance balance.

[0054] Plasma ball milling introduces appropriate amounts of edge defects, pore defects, and heteroatom doping into hard carbon precursors, thereby controlling the defect type and concentration to suitable levels. Untreated materials are typically dominated by disordered sp³ carbon, exhibiting poor conductivity and slow ion diffusion. Optimized materials form a conductive network dominated by sp² carbon, possessing uniform micro / mesopores and active sites, thereby: ① improving conductivity and reducing polarization; ② providing stable ion channels and enhancing rate performance; ③ improving reversible capacity through controllable defect adsorption; and ④ promoting the formation of a stable interfacial film and extending cycle life. This optimization is key to achieving a synergistic improvement in high capacity, high rate capability, and long cycle life.

[0055] The interlayer spacing of hard carbon refers to the average distance between its disordered carbon layers, with an optimal range typically of 0.36–0.40 nm. This size is slightly larger than that of graphite interlayer spacing, providing a stable intercalation space for larger sodium ions while promoting rapid ion diffusion. This enables synergistic sodium storage through adsorption and intercalation, thereby significantly improving reversible capacity and rate performance while ensuring structural stability.

[0056] In the hard carbon pre-oxidation process, defect concentration specifically refers to the density of introduced oxygen-containing functional groups (such as C=O and -COOH). The suitable parameters are typically an oxygen content of 5-15 at.%, existing in a covalently bonded form. Under these conditions, oxygen functional groups can act as polar active sites to enhance sodium ion adsorption capacity, improve interfacial wettability and ion diffusion kinetics, and guide the formation of a stable SEI film, thereby synergistically improving the material's reversible capacity, rate performance, and cycle stability. However, excessively high concentrations can damage the conductivity of the carbon framework and exacerbate side reactions; therefore, precise control through pre-oxidation is necessary to optimize performance.

[0057] This disclosure provides the application of bamboo-based hard carbon prepared by the above-described method in the negative electrode of a sodium-ion battery.

[0058] Example 1:

[0059] This disclosure provides a method for preparing a bamboo-based hard carbon anode material by plasma ball milling, comprising the following steps:

[0060] The precursor is selected from southern moso bamboo.

[0061] Natural bamboo pretreated with hydrochloric acid was subjected to pre-oxidation treatment at 300°C for 2 hours in air to obtain pre-oxidized bamboo powder.

[0062] Take 1.0 g of the pre-oxidized bamboo powder, place it in a ball mill jar, add zirconia grinding balls at a ball-to-material mass ratio of 20:1, and ball mill at 350 rpm for 15 minutes.

[0063] Subsequently, 0.50 g of the ball-milled powder was accurately weighed and placed in a tube furnace. Under an argon atmosphere, the temperature was raised to 1200°C at a heating rate of 5°C / min and calcined for 3 hours. After natural cooling, the bamboo-based hard carbon material was obtained.

[0064] Example 2:

[0065] Embodiment 2 of this disclosure provides a method for preparing a bamboo-based hard carbon anode material by plasma ball milling, comprising the following steps:

[0066] The precursor is selected from southern moso bamboo.

[0067] Natural bamboo pretreated with hydrochloric acid was subjected to pre-oxidation treatment at 300°C for 2 hours in air to obtain pre-oxidized bamboo powder.

[0068] Take 1.0 g of the pre-oxidized bamboo powder, place it in a ball mill jar, add zirconia grinding balls at a ball-to-material mass ratio of 20:1, and ball mill at 350 rpm for 5 minutes.

[0069] Subsequently, 0.50 g of the ball-milled powder was accurately weighed and placed in a tube furnace. Under an argon atmosphere, the temperature was raised to 1200°C at a heating rate of 5°C / min and calcined for 3 hours. After natural cooling, the bamboo-based hard carbon material was obtained.

[0070] Example 3:

[0071] Embodiment 3 of this disclosure provides a method for preparing a bamboo-based hard carbon anode material by plasma ball milling, comprising the following steps:

[0072] The precursor is selected from southern moso bamboo.

[0073] Natural bamboo pretreated with hydrochloric acid was subjected to pre-oxidation treatment at 300°C for 2 hours in air to obtain pre-oxidized bamboo powder.

[0074] Take 1.0 g of the pre-oxidized bamboo powder, place it in a ball mill jar, add zirconia grinding balls at a ball-to-material mass ratio of 20:1, and ball mill at 350 rpm for 30 minutes.

[0075] Subsequently, 0.50 g of the ball-milled powder was accurately weighed and placed in a tube furnace. Under an argon atmosphere, the temperature was raised to 1200°C at a heating rate of 5°C / min and calcined for 3 hours. After natural cooling, the bamboo-based hard carbon material was obtained.

[0076] Comparative Example 1:

[0077] Comparative Example 1 of this disclosure provides a method for preparing a bamboo-based hard carbon material, comprising the following steps:

[0078] The precursor is selected from southern moso bamboo.

[0079] Natural bamboo pretreated with hydrochloric acid was subjected to pre-oxidation treatment at 300°C for 2 hours in air to obtain pre-oxidized bamboo powder.

[0080] Subsequently, 0.50 g of the pre-oxidized powder was accurately weighed and placed in a tube furnace. Under an argon atmosphere, the temperature was raised to 1200°C at a heating rate of 5°C / min and calcined for 3 hours. After natural cooling, the bamboo-based hard carbon material was obtained.

[0081] Comparative Example 2:

[0082] Comparative Example 2 of this disclosure provides a method for preparing a bamboo-based hard carbon material, comprising the following steps:

[0083] The precursor is selected from southern moso bamboo.

[0084] Natural bamboo pretreated with hydrochloric acid was subjected to pre-oxidation treatment at 300°C for 2 hours in air to obtain pre-oxidized bamboo powder.

[0085] Take 1.0 g of the pre-oxidized bamboo powder, place it in a ball mill jar, add zirconia grinding balls at a ball-to-material mass ratio of 20:1, and ball mill at 350 rpm for 1 h.

[0086] Subsequently, 0.50 g of the ball-milled powder was accurately weighed and placed in a tube furnace. Under an argon atmosphere, the temperature was raised to 1200°C at a heating rate of 5°C / min and calcined for 3 hours. After natural cooling, the bamboo-based hard carbon material was obtained.

[0087] Comparative Example 3:

[0088] Comparative Example 3 of this disclosure provides a method for preparing a bamboo-based hard carbon material, comprising the following steps:

[0089] The precursor is selected from southern moso bamboo.

[0090] Natural bamboo pretreated with hydrochloric acid was subjected to pre-oxidation treatment at 300°C for 1 hour in air to obtain pre-oxidized bamboo powder.

[0091] Comparative Example 4:

[0092] Comparative Example 4 of this disclosure provides a method for preparing a bamboo-based hard carbon material, comprising the following steps:

[0093] The precursor is selected from southern moso bamboo.

[0094] Natural bamboo pretreated with hydrochloric acid was subjected to pre-oxidation treatment at 300°C for 3 hours in air to obtain pre-oxidized bamboo powder.

[0095] Physical characterization:

[0096] (1) X-ray diffraction (XRD) analysis

[0097] The crystal structure of the bamboo-based hard carbon materials in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 was characterized using an X-ray diffractometer (Bruker-D8-Advance type). The obtained XRD patterns are shown below. Figure 1 As shown, all samples exhibit distinct broadened "bun peaks" around 22° and 43°, corresponding to the (002) and (100) crystal planes of the carbon material, respectively. The appearance of such diffuse diffraction peaks indicates that the material has typical amorphous structural characteristics, consistent with the typical crystallographic properties of hard carbon.

[0098] (2) Nitrogen adsorption-desorption test

[0099] Samples with different ball milling times were systematically characterized by nitrogen adsorption-desorption tests. Figure 3 (a) All samples exhibit type IV isotherms and type H3 hysteresis loops, indicating mesoporous structure. BET test results show that the specific surface area of ​​the material increases significantly with increasing ball milling time: Comparative Example 1 has a specific surface area of ​​only 2.3 m²·g. - ¹, while Examples 1, 2, and 3 were increased to 7.6 m²·g. - ¹、16.9 m²·g - ¹ and 28.9 m²·g - ¹. Aperture distribution analysis ( Figure 3 (b) shows that as the ball milling time increased, the average pore size of Examples 1, 2, 3, and Comparative Example 1 remained stable at approximately 2 nm, but the total pore volume showed a systematic increasing trend, indicating that the pore volume of the material continuously expanded during the ball milling process, provided that the pore size remained basically unchanged. For hard carbon, precise control of specific surface area and micropore structure is crucial. While excessively high specific surface area increases sodium storage sites, it can also lead to side reactions, reduce first-efficiency, and hinder ion transport due to excessive micropores; conversely, excessively low specific surface area limits capacity improvement. Optimizing the pore structure through plasma ball milling can provide sufficient active sites while constructing channels dominated by mesopores, synergistically improving sodium storage capacity, ion kinetics, and cycling stability.

[0100] (3) Scanning electron microscopy (SEM) morphology test

[0101] The morphology of the bamboo-based hard carbon materials in Example 1, Comparative Example 1 and Comparative Example 2 was characterized using a Hitachi High-Tech SU8010 field emission scanning electron microscope.

[0102] Figure 2 The microstructures of bamboo-based hard carbon materials in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 are shown. All samples exhibit a dense, blocky sheet structure with irregular dimensions.

[0103] After plasma ball milling, the particle size and morphology of bamboo-based hard carbon were systematically regulated. With prolonged milling time, particle refinement exhibited a regular pattern: the untreated Comparative Example 1 sample had coarse particles (approximately 4 μm); after short-time milling (Example 1), the particle size significantly decreased to approximately 2 μm; further extended milling time (Examples 2 and 3) resulted in further particle refinement to approximately 1.5 μm and 1 μm, respectively, with the surface gradually exhibiting a loose and rough morphology, forming abundant wrinkles and pore structures. This synergistic evolution of "particle refinement – ​​surface roughening" effectively increased the contact area between the material and the electrolyte, providing more electrochemical active sites and facilitating improved ion diffusion and charge storage kinetics. However, longer milling time is not always better. When the milling time was excessively prolonged (Comparative Example 2, particle size decreased to approximately 0.5 μm), excessive pulverization and agglomeration of the particles occurred. Excessively fine particles can not only cause mechanical damage to the carbon layer structure, reducing the material's conductivity and structural stability, but also exacerbate side reactions due to their high specific surface area, affecting the electrode's compaction density and the continuity of ion transport channels, thus leading to a decline in electrochemical performance. Therefore, precise control of ball milling time is crucial for optimizing the microstructure and improving the overall performance of hard carbon materials.

[0104] Pre-oxidation plays a crucial role in regulating the mass retention and oxygen doping level of the material. Experimental data show that after 1 hour of pre-oxidation (Comparative Example 3), the mass retention was 52.9%; after 2 hours of pre-oxidation (Example 2), the mass retention stabilized at 52.3%; however, extending the time to 3 hours (Comparative Example 4) significantly reduced the mass retention to 44.4%. The results indicate that the pre-oxidation time needs to be controlled within a reasonable window (e.g., 1-2 hours). Too short a time (e.g., 1 hour) may maintain a high mass, but it is difficult to ensure sufficient oxygen atom introduction, affecting the subsequent construction of electrochemical active sites; too long a time will lead to excessive decomposition of the precursor, exacerbating mass loss and reducing structural stability. Therefore, achieving a balance between oxygen doping and mass retention is a necessary condition for optimizing material performance.

[0105] Application example:

[0106] Five groups of bamboo-based hard carbon samples were obtained, namely, those prepared in Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2.

[0107] Each sample was mixed with conductive agent (Super P conductive carbon black) and binder (polyvinylidene fluoride PVDF) in N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1, ground into a slurry, and then uniformly coated onto copper foil. The mixture was then placed in a vacuum oven and dried at 90°C for 12 h, and finally cut into circular electrode sheets with a diameter of 12 mm.

[0108] Using the aforementioned circular electrode as the negative electrode and a sodium plate as the counter electrode, the electrolyte was a 1 M solution of sodium trifluoromethyl sulfinate (NaSO3CF3) in diethylene glycol dimethyl ether (DEGDME), and the separator was a Whatman glass microfiber membrane. A coin cell was assembled in a glove box filled with argon atmosphere.

[0109] Electrochemical performance tests were conducted on coin cells assembled using bamboo-based hard carbon from Examples 1, 2, and 3 as negative electrode materials, as well as coin cells assembled using hard carbon prepared in Comparative Examples 1 and 2 as negative electrode materials.

[0110] 1A g -1 The specific capacity test at a current density of 150 cycles is currently the most common test current density and cycle number for sodium-ion batteries. Therefore, for ease of comparison, this disclosure uses the same current density and cycle number for testing. The maximum current density for rate performance testing is 2 A g. -1 This is also the most common current density for testing the rate performance of sodium-ion batteries, so this disclosure also uses the same maximum current density for rate performance testing.

[0111] (1) Ratio performance test

[0112] The concentrations were successively set at 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 2.0, and 0.2 A g. -1 Rate performance was tested at a current density of [value missing]. The test results are as follows: Figure 4 As shown.

[0113] At 0.2, 0.5, 1, 2, and 0.2 A·g - At a current density of ¹, the rate performance of the electrode materials of Example 1, Comparative Example 1, and Comparative Example 2 was tested. The results are as follows: Figure 4 As shown, Example 1 exhibits optimal rate performance under different current densities.

[0114] Table of mass loss percentage of bamboo charcoal before and after pre-oxidation

[0115]

[0116] Specifically, at 0.2, 0.5, 1.0, and 2.0 A·g - Under the specified conditions, the discharge specific capacities of Example 2 were 331.0, 305.3, 282.1, and 246.5 mAh·g, respectively. - ¹, significantly higher than in Example 1 (293.3, 268.3, 250.2, 229.4 mAh·g). - ¹) and Example 3 (265.1, 243.7, 228.3, 209.8 mAh·g) -¹). When the current density recovers to 0.2 A·g - ¹At that time, the capacity of Example 2 can be restored to 318.9 mAh·g - ¹, significantly higher than Example 1 (276.6 mAh·g) - ¹) and Example 3 (252.0 mAh·g) - ¹), indicating superior structural stability and electrochemical reversibility. The excellent rate performance of Example 1 is mainly due to the abundant porosity and defect structure introduced by the plasma ball milling process. These structural features not only effectively improve the electronic conductivity of the material and promote rapid charge migration, but also provide more active sites for sodium ions, significantly improving the Na+ ionization process. + The diffusion kinetics behavior was observed. In contrast, the capacities of Comparative Example 1 (un-plasma ball milled) were 234.5, 216.5, 199.8, 178.3 and 229.1 mAh·g⁻¹ after recovery. - ¹) The performance is significantly limited by the material's low intrinsic conductivity and limited ion diffusion pathways. The performance of Comparative Example 2 (plasma ball milling for 60 minutes, too long) is shown in the figures (226.5, 215.3, 196.3, 171.3 and the recovered 230.2 mAh·g). - ¹) Even lower than Comparative Example 1, which confirms that excessive ball milling leads to excessive crushing of the carbon skeleton, collapse of the pore structure and destruction of the conductive network, thereby severely degrading its rate performance and structural reversibility.

[0117] (2) Cyclic performance test

[0118] At 0.2 A g respectively -1 At low current density and 1 A g -1 Cyclic performance testing was conducted at high current densities.

[0119] At 0.2 Ag -1 The cycling performance test results at low current density are as follows: Figure 5 As shown.

[0120] from Figure 5 A comparison of electrochemical performance shows that bamboo-based hard carbon materials (Examples 1, 2, 3) treated with plasma ball milling for different times exhibit better performance at 0.2 A g. - ¹After 50 cycles at current densities, its reversible capacity (250.1, 303.8, and 204.4 mAh g, respectively) - ¹) Both were significantly higher than those of Comparative Example 1 (176.5 mAh g) without ball milling treatment. -¹), demonstrating the crucial role of plasma ball milling in enhancing the sodium storage performance of the material. Notably, when the ball milling time was controlled at 15 minutes (Example 2), the material exhibited optimal electrochemical performance, with the highest reversible capacity (303.8 mAh g⁻¹). - ¹), indicating that the processing time effectively optimized the material structure while avoiding excessive damage. However, when the ball milling time was further extended (Comparative Example 2), the material capacity (177.4 mAh g⁻¹) decreased. - ¹) Instead, it dropped to a level comparable to that of the untreated sample, which confirms that excessive ball milling time leads to over-grinding of the carbon skeleton or excessive accumulation of defects, thereby destroying its sodium-storing active structure.

[0121] To investigate the stability and durability of the electrodes under high current density, 1 A g was applied to three groups of electrodes respectively. -1 High current density, test results as follows Figure 6 As shown, the bamboo-based hard carbon electrodes of Examples 2, 1, 3, 1, and 2 still exhibited 254.9, 203.9, 193.8, 150.2, and 164.4 mAh g⁻¹ respectively after 150 cycles. -1 The capacity. Similarly, Example 1 exhibited the best electrochemical performance.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing bamboo-based hard carbon anode material by plasma ball milling, characterized in that, Includes the following steps: S1. Cut natural bamboo into pieces, first use dilute hydrochloric acid to acid wash to remove inorganic ash inside and on the surface of the bamboo, then use deionized water and anhydrous ethanol alternately for ultrasonic cleaning, and then dry at 60-80℃ to obtain pretreated bamboo precursor. S2. Bamboo precursor is heated to 300°C in air at a heating rate of 2°C / min and held for 2 h to obtain pre-oxidized bamboo powder. The oxygen content of the pre-oxidized bamboo powder is 5-15 at.%, and it exists in a covalent bond form. S3. Pre-oxidized bamboo powder is subjected to planetary plasma ball milling for 5-30 minutes under a protective atmosphere, a ball-to-particle mass ratio of (10-20):1, and a rotation speed of 300-500 rpm, so that the particle size is controlled at 1 µm-2 µm. The carbon skeleton structure is optimized through the synergistic effect of pre-oxidation and plasma ball milling. S4. The ball-milled powder is heated to 1000-1300℃ at a heating rate of 5℃ / min and held at that temperature for 1-3 h under an argon protective atmosphere to obtain a bamboo-based hard carbon anode material through high-temperature carbonization; the interlayer spacing of the bamboo-based hard carbon anode material is 0.36-0.40 nm, and the specific surface area is 5-30 m². 2 / g; In step S3, the protective atmosphere is argon, an argon-hydrogen mixture, hydrogen, or nitrogen.

2. The method for preparing a bamboo-based hard carbon anode material by plasma ball milling according to claim 1, characterized in that, In step S3, an intermittent ball milling mode is used, running for 5-10 minutes and pausing for 5-10 minutes.

3. The method for preparing a bamboo-based hard carbon anode material by plasma ball milling according to claim 1, characterized in that, In step S4, the final temperature of the high-temperature carbonization is 1200°C, and the holding time is 3 hours.

4. The method for preparing a bamboo-based hard carbon anode material by plasma ball milling according to claim 1, characterized in that, The natural bamboo mentioned is the southern moso bamboo of Fujian, which has a growth cycle of 3-5 years.

5. A bamboo-based hard carbon anode material produced by plasma ball milling, characterized in that, The bamboo-based hard carbon anode material prepared by any one of claims 1 to 4.

6. The application of a bamboo-based hard carbon anode material milled by plasma ball milling, characterized in that, The bamboo-based hard carbon anode material prepared by any one of claims 1 to 4 or the bamboo-based hard carbon anode material described in claim 5 is applied to the anode of a sodium-ion battery.

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