Bamboo-based large-interlayer-spacing homogeneous graphite-like subcrystalline carbon material as well as preparation method and application thereof

Abstract

The invention discloses a bamboo-based large-interlayer-spacing homogeneous graphite-like sub-crystal carbon material and a preparation method and application thereof, the bamboo-based large-interlayer-spacing homogeneous graphite-like sub-crystal carbon material comprises a homogeneous graphite-like sub-crystal carbon material, and the homogeneous graphite-like sub-crystal carbon material is characterized by being composed of 3.714.0 large-interlayer-spacing approximately-parallel oriented carbon sheets. When the homogeneous graphite-like subcrystal carbon material is used for a sodium ion battery negative electrode, the initial coulombic efficiency reaches 94.4%, the initial charging specific capacity reaches 353.5 mAh / g, and the performance is comparable with that of a lithium battery graphite negative electrode. The preparation method comprises the following steps: by taking bamboo wood as a precursor, fully inducing a macroscopic bamboo wood continuum to generate an oxygen-containing six-membered ring network intermediate product by taking a graphite container and graphite powder as double seed crystals at low temperature; and inducing an intermediate product with a proper particle size at a high temperature by taking a graphite container as a single crystal seed to prepare the graphite-like subcrystal carbon material with a uniform structure. The method takes a bamboo source as a raw material, is simple in process and low in energy consumption, and has remarkable industrialization potential.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials technology, specifically relating to a bamboo-based homogeneous graphite subcrystalline carbon material with large interlayer spacing, its preparation method, and its application. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries, leveraging the abundant sodium resources, have broad application prospects in large-scale energy storage power stations. However, the research and development of sodium-ion battery anode materials has lagged significantly, becoming a key bottleneck restricting performance breakthroughs and industrialization. The energy density of a full battery at the active material level is mainly determined by the average operating voltage difference between the positive and negative electrodes and their reversible capacity after matching. During full battery discharge, the anode undergoes sodium removal. Therefore, when evaluating carbon anode materials based on half-cell testing, efforts should be made to improve their reversible sodium removal capacity (first charge specific capacity = 'first discharge specific capacity × first coulombic efficiency'), increase the proportion of first charge capacity in the low-voltage plateau region, and improve the first coulombic efficiency to maximize the full battery energy density. For the anode, a low first charge capacity will reduce the battery's energy density; while a low first coulombic efficiency will lead to irreversible loss of active sodium, which must be compensated for in actual production through excess positive electrode or pre-sodiumization design, but this will significantly increase material costs and reduce the battery's actual energy density.

[0003] Hard carbon materials prepared using biomass as a precursor have become a research hotspot for sodium-ion battery anode materials due to their wide availability of raw materials, low cost, and high specific capacity (≥300 mAh / g). However, the microstructure of traditional biomass-based hard carbon is a disordered layer structure formed by randomly oriented and distorted carbon sheets stacked together, with numerous defects and pores. These disordered layers, defects, and pores lead to irreversible insertion / adsorption of sodium ions: on the one hand, forming a high-potential slope region with a high proportion of capacity; on the other hand, causing significant irreversible capacity loss, ultimately resulting in an initial coulombic efficiency far lower than that of graphite anodes in commercial lithium-ion batteries. Among biomass raw materials, bamboo is widely considered a sustainable biomass precursor for preparing carbon anode materials for sodium-ion batteries due to its short growth cycle, abundant resources, ease of collection and transportation, and dense arrangement of natural fibers. However, traditional pyrolysis methods usually yield hard carbon with disordered structures, which limits its performance.

[0004] In the prior art, patent CN117658107A discloses a method for preparing bamboo-based hard carbon. In the electrochemical performance test of sodium-ion batteries, the bamboo-based hard carbon material has an initial coulombic efficiency of 81.1%-89.8% and an initial discharge specific capacity of 293.5-339.7 mAh / g. Among them, Example 2 (89.8%) has the best initial coulombic efficiency and corresponds to an initial discharge specific capacity of 323.2 mAh / g, while Example 6 (339.7 mAh / g) has the best initial discharge specific capacity and corresponds to an initial coulombic efficiency of 81.1%.

[0005] In the industrial application of sodium-ion batteries, their carbon anode materials must at least reach the same level of lithium storage as graphite anodes in lithium-ion batteries (according to the national standard GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries", the initial coulombic efficiency of graphite anodes must be ≥ 90%; the "Lithium-ion Battery Industry Standard Conditions (2024 Edition)" specifies that the specific capacity of graphite must be ≥ 340mAh / g). Therefore, the development of novel high-performance bamboo-based carbon anode materials that combine high initial coulombic efficiency and high initial charge specific capacity is of great significance to the development and application of sodium-ion batteries. Summary of the Invention

[0006] To overcome the problems existing in the prior art, one objective of this invention is to provide a bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing. A second objective is to provide a method for preparing the aforementioned bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing. A third objective is to provide applications of the aforementioned bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing. A fourth objective is to provide a battery negative electrode. A fifth objective is to provide a sodium-ion battery.

[0007] This invention uses bamboo with high cellulose content as a precursor. Addressing the characteristic of bamboo undergoing extensive pyrolysis and concentrated removal of hydrogen and nitrogen-containing groups, it innovatively employs a key step of "low-temperature double seeding (graphite container + graphite powder) to fully and continuously induce a macroscopic bamboo matrix." This utilizes the continuous contact of the macroscopic bamboo matrix to avoid the discontinuous defects induced by powder, inducing the formation of a continuous oxygen-containing six-membered ring network. Through the oxygen-containing lattice memory effect, it fully topologically topologically ordered frameworks with large interlayer spacings of cellulose, laying the foundation for the subsequent formation of a homogeneous structure. Subsequently, a process design of "high-temperature single seeding to induce intermediate product powder of appropriate particle size" is used to balance the pyrolysis efficiency of oxygen-containing groups with the appropriate carbon-oxygen substitution, simultaneously performing lattice repair to avoid over-induction of graphite impurities and disordered structures. This successfully prepares a structure with uniform structure and interlayer spacing adaptable across the entire range (3.71-4.0). The bamboo-based graphite subcrystalline carbon material with no impurities (Å) finally achieved a high reversible capacity (353.5 mAh / g) and a high first coulombic efficiency (94.4%) comparable to the high-level performance of lithium-ion battery graphite. At the same time, it significantly reduced the high-temperature processing temperature and residence time compared with existing solutions, reduced the energy consumption of preparation, and has outstanding cost advantages and industrialization potential.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing. The phase of this material is graphite-like subcrystalline carbon; its structure is a homogeneous structure composed of nearly parallel, long-range oriented carbon sheets. Its (002) interplanar spacing d 002 The range is 3.71–4.0 Å.

[0009] Among them, the inter-face spacing d 002 Based on statistical measurements using transmission electron microscopy (TEM).

[0010] Preferably, the bamboo-based, large-interlayer-spacing homogeneous graphite-like subcrystalline carbon material exhibits broadened and diffused diffraction spots in electron diffraction, lacking the sharp, regular lattice of single-crystal materials and the completely diffuse halos of amorphous materials; its XRD pattern shows broadened envelope peaks, and Raman surface scanning reveals I... D / I G The ratio distribution is uniform, exhibiting typical subcrystalline characteristics.

[0011] Preferably, the bamboo-based homogeneous graphite subcrystalline carbon material with large interlayer spacing does not contain graphite phase, hard carbon phase, or disordered carbon sheet stacking structure (including fracture, large-angle bending, and turbine-shaped carbon sheet stacking), and has no random orientation defects.

[0012] The second aspect of this invention provides a method for preparing the bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing described in the first aspect, comprising the following steps: Bamboo material was placed in a sealed graphite container filled with graphite powder, and the first induced growth reaction was carried out to obtain bamboo-based subcrystalline carbon intermediate. The bamboo-based subcrystalline carbon intermediate product is pulverized to obtain powdered bamboo-based subcrystalline carbon intermediate product; impurities in the bamboo-based subcrystalline carbon intermediate product are removed to obtain purified powdered bamboo-based subcrystalline carbon intermediate product. The purified powdered bamboo-based subcrystalline carbon intermediate was placed in a sealed graphite container and subjected to a second induced growth reaction to obtain the bamboo-based homogeneous graphite subcrystalline carbon material with large interlayer spacing.

[0013] Preferably, the graphite filling refers to the graphite filling the gaps inside the graphite container and completely encapsulating the bamboo material.

[0014] Preferably, the bamboo material includes raw bamboo material, processed bamboo products, and bamboo processing waste. More preferably, the raw bamboo material includes whole culms, sections, and branches of bamboo species such as moso bamboo, nan bamboo, ci bamboo, and light bamboo. More preferably, the processed bamboo products include bamboo skewers, bamboo chopsticks, etc.

[0015] Preferably, the process further includes the following steps: after the first induced growth reaction, the reaction product is washed and dried to obtain a bamboo-based subcrystalline carbon intermediate product.

[0016] More preferably, the cleaning includes sequentially cleaning with water and ethanol to remove graphite powder adhering to the surface; More preferably, the drying is performed at 70-90°C.

[0017] Preferably, the reaction conditions for the first induced growth reaction include at least one of the following: a) The reaction temperature is 400-600℃; b) The heat preservation time is 1-3 hours; c) Heat to the reaction temperature at a heating rate of 0.5~5 ℃ / min; d) The reaction is carried out under a protective atmosphere.

[0018] More preferably, the reaction temperature is 450-550°C.

[0019] More preferably, the protective atmosphere is argon.

[0020] Preferably, the reaction conditions for the second induced growth reaction include at least one of the following: A) The reaction temperature is 1400-1600℃; B) The heat preservation time is 2-4 hours; C) Heat to the reaction temperature at a heating rate of 0.5~5 ℃ / min; D) The reaction is carried out under a protective atmosphere.

[0021] More preferably, the reaction temperature is 1400-1500℃.

[0022] More preferably, the protective atmosphere is argon.

[0023] Preferably, the particle size of the powdered bamboo-based subcrystalline carbon intermediate is 10~60 μm.

[0024] Preferably, the process includes the following steps: soaking the powdered bamboo-based subcrystalline carbon intermediate product in acid and / or alkali to remove impurities from the powdered bamboo-based subcrystalline carbon intermediate product.

[0025] More preferably, step S2 is: the powdered bamboo-based subcrystalline carbon intermediate is sequentially soaked in acid, soaked in alkali, and soaked in acid again, and then washed and dried to obtain purified powdered bamboo-based subcrystalline carbon intermediate.

[0026] More preferably, the acid is selected from at least one of sulfuric acid, hydrochloric acid, nitric acid, formic acid, and acetic acid.

[0027] More preferably, the alkali is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0028] More preferably, specifically: the powdered bamboo-based subcrystalline carbon intermediate product is sequentially processed using 1... 5 mol / L hydrochloric acid solution, 4 8 mol / L sodium hydroxide solution and 4 Soak in 8 mol / L sulfuric acid solution for 2 12h to remove metal oxides / salts and amorphous silica impurities from bamboo-based subcrystalline carbon intermediates.

[0029] Preferably, the sealed graphite container includes one of a graphite crucible and a graphite boat.

[0030] Preferably, the graphite powder has a particle size of 0.3-0.8 μm.

[0031] The third aspect of this invention provides the application of the bamboo-based homogeneous graphite subcrystalline carbon material with large interlayer spacing described in the first aspect in battery active materials.

[0032] A fourth aspect of the present invention provides a battery negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising the bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing described in the first aspect.

[0033] Preferably, the negative electrode current collector is a metal foil.

[0034] Preferably, the negative electrode active layer comprises a homogeneous graphite-like subcrystalline carbon material with large interlayer spacing, a solvent, and a binder.

[0035] More preferably, the solvent is water.

[0036] The fifth aspect of the present invention provides a sodium-ion battery, comprising the negative electrode sheet described in the fourth aspect.

[0037] The beneficial effects of this invention are: This invention provides a bamboo-based, large-interlayer-spacing homogeneous graphite-like subcrystalline carbon material, comprising a homogeneous graphite-like subcrystalline carbon material, wherein the material is composed of 3.71... The large interlayer spacing of 4.0 Å and the near-parallel, long-range aligned carbon sheets constitute a homogeneous subcrystalline structure. When this homogeneous graphite-like subcrystalline carbon material is used as an anode in sodium-ion batteries, the initial coulombic efficiency reaches 94.4%, and the initial charge specific capacity reaches 353.5 mAh / g, with performance comparable to that of graphite anodes in lithium-ion batteries.

[0038] This invention also provides a method for preparing the aforementioned bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing. Using bamboo as a precursor, and considering its concentrated pyrolysis near the pyrolysis peak, the method first induces the formation of an oxygen-containing six-membered ring network intermediate product from the macroscopic bamboo continuum at low temperature using a graphite container and graphite powder as seed crystals. This intermediate product inherits the ordered framework of cellulose with large interlayer spacing through the oxygen-containing lattice memory effect. Then, at high temperature, using a graphite container as a single seed crystal, the method induces intermediate product powder of appropriate particle size to balance the pyrolysis efficiency of oxygen-containing groups and the appropriateness of carbon-oxygen substitution, avoiding disordered carbon sheet stacking and random orientation defects. Finally, a structurally homogeneous graphite-like subcrystalline carbon material is obtained. This method is simple, energy-efficient, and has significant industrialization potential.

[0039] Figure caption Figure 1 Characterization spectra of bamboo-based precursors and related products: (a) X-ray diffraction (XRD) pattern of bamboo-based precursors; (b) differential thermogravimetric curve of bamboo-based precursors; (c) infrared spectrum of bamboo-based precursors; (d) infrared spectra of intermediate product (curve I) and target product bamboo-based subcrystalline carbon material (curve II) after low-temperature induction in Example 1.

[0040] Figure 2 Transmission electron microscopy (TEM) characterization images of the bamboo-based subcrystalline carbon material prepared in Example 1: (a) Low-magnification TEM image and selected area electron diffraction (SAED) spectrum; (bf) High-resolution TEM (HRTEM) image.

[0041] Figure 3XRD patterns of typical embodiments and comparative examples: (a) Example 1; (b) Example 2; (c) Comparative Example 1; (d) Comparative Example 2; (e) Comparative Example 3; (f) Comparative Example 4; (g) Comparative Example 5; (h) Comparative Example 6; (i) Comparative Example 8.

[0042] Figure 4 X-ray photoelectron spectroscopy (XPS) plots for typical embodiments and comparative examples, and A sp² / A sp³ Comparative bar charts: (a, b) XPS total spectrum and high-resolution C1s spectrum of Example 1; (c) High-resolution C1s spectrum of Example 2; (d) High-resolution C1s spectrum of Comparative Example 1; (e) High-resolution C1s spectrum of Comparative Example 2; (f) High-resolution C1s spectrum of Comparative Example 3; (g) A spectrum of Examples 1, 2, and Comparative Examples 1-3. sp² / A sp³ Comparison bar charts; (h) High-resolution C1s spectrum of Comparative Example 4; (i) High-resolution C1s spectrum of Comparative Example 5; (j) High-resolution C1s spectrum of Comparative Example 6; (k) High-resolution C1s spectrum of Comparative Example 7; (l) High-resolution C1s spectrum of Comparative Example 8.

[0043] Figure 5 TEM images of typical comparative samples: (ac) TEM image (including SAED image corresponding to the inset) and HRTEM image of Comparative Example 2; (dm) TEM image (including SAED image corresponding to the inset) and HRTEM image of Comparative Example 4, the sub-images corresponding to its composite structure are: (df) quasi-graphite crystals, (g) graphite phase, (h, i) graphite subgrains, (jm) fractured and large-angle bent corrugated carbon sheet stacked structure; (n, o) TEM image (including SAED image corresponding to the inset) and HRTEM image of hard carbon in Comparative Example 8.

[0044] Figure 6 Raman surface scans of Example 1 and Comparative Example 4 D / I G Ratio distribution diagram and representative spectrum: (a) Raman I of Example 1 D / I G (a) Ratio surface scan; (b) Typical Raman spectrum of Example 1 extracted from region I in Figure (a); (c) Raman I of Comparative Example 4 D / I G Ratio surface scan; (d) Typical Raman spectra of Comparative Example 4 extracted from corresponding regions I-IV in Figure (c) (spectral I-IV correspond to regions I-IV respectively).

[0045] Figure 7N2 adsorption-desorption isotherms for Example 1 and Comparative Example 8: (a) Example 1; (b) Comparative Example 8.

[0046] Figure 8 The following are the first discharge-charge curves and performance comparison bar charts for typical examples and comparative examples: (a) Example 1; (b) Example 2; (c) Comparative Example 1; (d) Comparative Example 2; (e) Comparative Example 3; (f) First charge specific capacity comparison bar chart for Examples 1, 2, and Comparative Examples 1-3; (g) First coulombic efficiency comparison bar chart for Examples 1, 2, and Comparative Examples 1-3; (h) Comparative Example 4; (i) Comparative Example 5; (j) Comparative Example 6; (k) Comparative Example 7; (l) Comparative Example 8. Detailed Implementation

[0047] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from conventional commercial channels or prepared and isolated through simple synthesis; unless otherwise specified, the processes employed are conventional processes in the art.

[0048] Example 1 This example provides a method for preparing bamboo-based subcrystalline carbon materials, specifically the following steps: Step (1): Take commercially available bamboo sticks, remove the pointed ends, cut a stick-shaped segment with a diameter of 0.12 cm and a length of 5.00 cm, first wash the surface with deionized water to remove impurities, and then dry it at 70 ℃ for 12 h to obtain pre-treated bamboo stick segments.

[0049] Step (2): Take 50 pretreated bamboo skewer segments obtained in step (1) (total mass 3.20 ± 0.2 g), place them in a 10 mL graphite crucible, and then fill in 2.0 g of graphite powder (particle size D). 50 <0.6 μm), ensuring that the graphite powder fills the voids inside the crucible and completely coats the bamboo skewer segments. Cover with a graphite cap to create a sealed space inside the crucible. Place the sealed graphite crucible in a tube furnace, introduce argon as a protective gas, and heat to 500 ℃ at a heating rate of 2 ℃ / min for low-temperature induced growth for 2 h (graphite crucible + graphite powder double seed induction). After cooling to room temperature, remove the product and ultrasonically clean it three times with deionized water and anhydrous ethanol to thoroughly remove the graphite powder adhering to the surface. Filter and collect the product, and dry it at 70 ℃ for 12 h to obtain the bamboo-based subcrystalline carbon intermediate product.

[0050] Step (3): Take the bamboo-based subcrystalline carbon intermediate obtained in step (2), grind it manually in an agate mortar for 10 minutes, and pass it through a 50-mesh sieve to obtain the average particle size (D). 50It is a 57.1 μm powdered bamboo-based subcrystalline carbon intermediate.

[0051] Step (4): Take the powdered bamboo-based subcrystalline carbon intermediate obtained in step (3) and subject it to acid and alkali soaking treatments in sequence to remove impurities: First, add 2 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:100 (g:mL) and soak for 24 h; then replace with 6 mol / L sodium hydroxide solution (same solid-liquid ratio) and soak for 24 h; finally replace with 6 mol / L sulfuric acid solution (same solid-liquid ratio) and soak for 24 h to remove metal oxides / salts and amorphous silica impurities in the bamboo-based subcrystalline carbon intermediate. After soaking, ultrasonically wash the product three times (10 min each time) with deionized water and anhydrous ethanol in sequence to thoroughly remove residual acid and alkali solutions and impurities; filter and collect the product, and dry it at 70 ℃ for 12 h to obtain purified bamboo-based subcrystalline carbon intermediate.

[0052] Step (5): Take 0.50 g of the powdered purified bamboo-based subcrystalline carbon intermediate obtained in step (4), place it in a 10 mL graphite crucible, cover it with a graphite lid to form a sealed space (but do not add graphite powder), then place the crucible in a tube furnace, and heat it to 1500 ℃ at a heating rate of 0.5 ℃ / min under argon protection, and induce growth at high temperature for 4 h (graphite crucible single crystal seed induction); cool it to room temperature to obtain bamboo-based subcrystalline carbon material.

[0053] The bamboo-based subcrystalline carbon material prepared in this example was used as the negative electrode active material to assemble a CR2032 coin cell sodium-ion battery, and its electrochemical performance was tested. The specific steps are as follows: Step (6): Take the bamboo-based subcrystalline carbon material (active substance) obtained in Example 1 and sodium alginate (binder), mix them in a mass ratio of 95:5, use pure water as solvent, and manually grind the mixture until a slurry with uniform texture and no obvious particle agglomeration is formed.

[0054] Step (7): Take the slurry obtained in step (6) and apply it evenly to the flat copper foil surface using a coater with a gap of 100 μm. Then, place the coated copper foil in a vacuum drying oven at 120 ℃ and dry it for 24 h. After drying, take it out and cut it into circular electrode sheets with a diameter of 14 mm.

[0055] Step (8): Take the electrode sheet obtained in step (7) as the working electrode, the sodium metal sheet as the counter electrode, the glass fiber membrane as the separator, and the electrolyte is a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) with 1 mol / L NaClO4 (EC and DMC volume ratio is 1:1). In a glove box with water oxygen content below 0.1 ppm, assemble the CR2032 button sodium ion half cell in the order of working electrode, separator, electrolyte wetting, and counter electrode.

[0056] Step (9): The sodium-ion half-cell assembled in step (8) was placed in a constant temperature environment of 25 ℃, and a discharge-charge curve test was performed using a battery tester at a voltage range of 0.01-3 V and a current density of 20 mA / g. The measured first charge specific capacity was 353.5 mAh / g, and the first coulombic efficiency was 94.4%.

[0057] Example 2 This example provides a method for preparing bamboo-based subcrystalline carbon, which differs from Example 1 only in step (3): after manual grinding for 10 min and passing through a 50-mesh sieve, a ball milling process is added (ball mill speed 350 r / min, time 2 h). The average particle size (D) of the resulting powdered bamboo-based subcrystalline carbon intermediate product is... 50 The thickness is 13.6 μm. The remaining steps and parameters are exactly the same as in Example 1. The test method is the same as in Example 1, with an initial charge specific capacity of 342.0 mAh / g and an initial coulombic efficiency of 90.2%.

[0058] Example 3 This example provides a method for preparing bamboo-based subcrystalline carbon, which differs from Example 1 only in step (3): after manual grinding for 10 min and passing through a 50-mesh sieve, a ball milling process is added (ball mill speed 500 r / min, time 30 min). The average particle size (D) of the resulting powdered bamboo-based subcrystalline carbon intermediate product is... 50 The thickness was 37.7 μm. The remaining steps and parameters were exactly the same as in Example 1. The test method was the same as in Example 1, with an initial charge specific capacity of 340.4 mAh / g and an initial coulombic efficiency of 93.6%.

[0059] Example 4 This example provides a method for preparing bamboo-based subcrystalline carbon, which differs from Example 1 only in that the high-temperature induction time in step (5) is changed from 4 h to 3 h. The remaining steps and parameters are exactly the same as in Example 1. The testing method is the same as in Example 1, with an initial charge specific capacity of 347.9 mAh / g and an initial coulombic efficiency of 90.1%.

[0060] Example 5 This example provides a method for preparing bamboo-based subcrystalline carbon, which differs from Example 1 only in that the high-temperature induction temperature in step (5) is changed from 1500 ℃ to 1400 ℃. All other steps and parameters are exactly the same as in Example 1. The testing method is the same as in Example 1, with an initial charge specific capacity of 349.7 mAh / g and an initial coulombic efficiency of 90.2%.

[0061] Comparative Example 1 This example provides a method for preparing bamboo-based derived carbon, which differs from Example 2 only in the ball milling time in step (3): changing 2 h to 4 h, resulting in an average particle size (D) of the powdered bamboo-based subcrystalline carbon intermediate. 50 The thickness is 6.0 μm. The remaining steps and parameters are exactly the same as in Example 2. The test method is the same as in Example 1, with an initial charge specific capacity of 331.9 mAh / g and an initial coulombic efficiency of 90.1%.

[0062] Comparative Example 2 This example provides a method for preparing bamboo-based derived carbon, which differs from Example 2 only in the ball milling time in step (3): changing 2 h to 6 h, resulting in an average particle size (D) of the powdered bamboo-based subcrystalline carbon intermediate. 50 The thickness was 4.2 μm. The remaining steps and parameters were exactly the same as in Example 2. The testing method was the same as in Example 1, with an initial charge specific capacity of 326.1 mAh / g and an initial coulombic efficiency of 90.3%.

[0063] Comparative Example 3 This example provides a method for preparing bamboo-based derived carbon with poor electrochemical performance. The only difference between this method and Example 1 is step (3): the manual grinding time is shortened from 10 min to 5 min, and the average particle size (D) of the resulting powdered bamboo-based derived carbon intermediate product is reduced. 50 The thickness was 62.1 μm. Other steps and parameters were exactly the same as in Example 1. The test method was the same as in Example 1, with an initial charge specific capacity of 332.3 mAh / g and an initial coulombic efficiency of 91.6%.

[0064] Comparative Example 4 This example provides a bamboo-based composite carbon material (containing quasi-graphite crystals, graphite phases, graphite subgrains, and a corrugated carbon sheet stack structure with fractures and large-angle bending). The core difference between its preparation method and Example 1 lies in the following: it employs double-seed induction throughout the process (graphite crucible + graphite powder), does not grind or sieve after low-temperature carbonization, and continues to fill with graphite powder during high-temperature treatment to achieve continuous induction. Specifically, as follows: Step (1): exactly the same as step (1) in Example 1.

[0065] Step (2): The process is exactly the same as step (2) in Example 1. After cooling to room temperature, the bamboo-based composite carbon intermediate product is collected (after cleaning to remove surface graphite powder and drying, without grinding or sieving).

[0066] Step (3): The unground macroscopic continuous bamboo-based composite carbon intermediate obtained in step (2) is directly purified. The remaining processes are exactly the same as step (4) of Example 1 (without grinding and sieving steps), and the purified bamboo-based carbon intermediate is still a macroscopic continuous.

[0067] Step (4): Take the purified product (macroscopic continuum, unground into powder) obtained in step (3), place it in a 10 mL graphite crucible, and fill it with 2.0 g of graphite powder (particle size D). 50 <0.6 μm) and sealed with a cap, the remaining process parameters are the same as step (5) of Example 1. After cooling to room temperature, the surface graphite powder is removed by cleaning, dried, manually ground for 10 min and passed through a 50-mesh sieve to obtain an average particle size (D 50 The material is a 50.6 μm powdered bamboo-based composite carbon material. The testing method was the same as in Example 1. The initial charge specific capacity was 324.5 mAh / g, and the initial coulombic efficiency was 89.5%.

[0068] Comparative Example 5 This example provides a bamboo-based derived carbon material. The core difference between its preparation method and that of Example 1 is that the macroscopic continuous morphology of the precursor and carbon intermediate products is maintained throughout the process (no grinding and sieving steps, replacing the powder morphology used in the high-temperature induction of Example 1), and single-crystal seed induction is used throughout the process (only a graphite crucible, without graphite powder synergy), as detailed below: Step (1): exactly the same as step (1) in Example 1.

[0069] Step (2): The process is exactly the same as step (2) in Example 1. After cooling to room temperature, the bamboo-based derived carbon intermediate (macroscopic continuous morphology, unground) is collected.

[0070] Step (3): The unground macroscopic continuous bamboo-based carbon intermediate obtained in step (2) is directly purified. The remaining processes are exactly the same as step (4) of Example 1 (without grinding and sieving steps), and the purified bamboo-based carbon intermediate is still a macroscopic continuous.

[0071] Step (4): Take the purified product (macroscopic continuum, unground into powder) obtained in step (3), place it in a 10 mL graphite crucible and cover it to form a sealed space. The remaining process parameters are the same as in step (5) of Example 1. After cooling to room temperature, wash and dry it, grind it manually for 10 min and pass it through a 50-mesh sieve to obtain an average particle size (D). 50The material is a bamboo-based carbon material with a thickness of 43.4 μm. The testing method is the same as in Example 1. The initial charge specific capacity is 307.0 mAh / g, and the initial coulombic efficiency is 89.0%.

[0072] Comparative Example 6 This example provides a bamboo-based derived carbon material, the core difference from Example 1 being: the use of powdered bamboo-based precursor in the low-temperature stage (replacing the macroscopic continuum precursor), and the entire process involving single-crystal seed induction (using only a graphite crucible, without graphite powder synergy), as detailed below: Step (1): Take commercially available bamboo sticks, remove the pointed ends, cut into stick segments with a diameter of 0.12 cm and a length of 5.00 cm, clean the surface impurities, grind them in a grinder for 10 minutes and pass them through a 50-mesh sieve (average particle size D of fine powder). 50 = 45.6 μm), the rest of the process is exactly the same as step (1) of Example 1.

[0073] Step (2): Take 3.30 g of the powdered precursor obtained in step (1), put it into a 10 mL graphite crucible and cover it (without graphite powder filling). The rest of the process is the same as step (2) in Example 1. After cooling to room temperature, bamboo-based derived carbon intermediate is obtained.

[0074] Step (3): Same as step (4) in Example 1, to obtain purified powdered bamboo-based derived carbon intermediate.

[0075] Step (4): Take the purified product obtained in step (3), put it into a 10 mL graphite crucible and cover it (without graphite powder filling). The remaining process is the same as step (5) in Example 1. After cooling to room temperature, bamboo-based derived carbon material is obtained. The test method is the same as in Example 1. The first charge specific capacity is 316.4 mAh / g and the first coulombic efficiency is 89.7%.

[0076] Comparative Example 7 This example provides a bamboo-based derived carbon material containing graphite powder. The only difference between this material and Comparative Example 6 is that in step (2), 5% of the graphite powder (particle size D50 < 0.6 μm) is added to the powdered precursor and mixed evenly. The remaining steps and parameters are exactly the same as those in Comparative Example 6. Graphite powder is added to the powdered bamboo-based precursor at the low-temperature stage, and full-process double seeding (graphite crucible + graphite powder) is used to supplement the variable gap of "powdered + full-process single seeding" in Comparative Example 6. The test method is the same as in Example 1. The initial charge specific capacity is 309.1 mAh / g, and the initial coulombic efficiency is 92.4%.

[0077] Comparative Example 8 This example provides a bamboo-based hard carbon material. The core difference between its preparation method and that of Example 1 is that graphite seed crystals are not used throughout the entire process (no graphite crucible or graphite powder is used). Instead, a magnesium oxide crucible and matching lid are used for heat treatment. The remaining processes are completely the same, as detailed below: Step (1): exactly the same as step (1) in Example 1.

[0078] Step (2): Take 50 pretreated bamboo skewers (total mass 3.20 ± 0.2 g) obtained in step (1), put them into a 10 mL magnesium oxide crucible and cover it to form a sealed space. The remaining process parameters are the same as in step (2) of Example 1. After cooling to room temperature, collect the bamboo-based carbon intermediate product (no need to remove graphite powder).

[0079] Step (3): Place the bamboo-based carbon intermediate obtained in step (2) into an agate mortar and grind it manually for 10 minutes. Then pass it through a 50-mesh sieve to obtain powdered carbon intermediate.

[0080] Step (4): The same as step (4) in Example 1, to obtain purified bamboo-based carbon intermediate.

[0081] Step (5): Take the purified bamboo-based carbon intermediate obtained in step (4), put it into a 10 mL magnesium oxide crucible and cover it. The remaining process parameters are the same as in step (5) of Example 1. After cooling to room temperature, bamboo-based hard carbon material is obtained. The test method is the same as in Example 1. The first charge specific capacity is 298.8 mAh / g and the first coulombic efficiency is 86.3%.

[0082] Comparative Example 9 This example provides a bamboo-based derived carbon material, which differs from Example 1 only in the high-temperature induction time of step (5): extended from 4 h to 5 h. The remaining steps and parameters are exactly the same as in Example 1. The test method is the same as in Example 1, with an initial charge specific capacity of 327.6 mAh / g and an initial coulombic efficiency of 90.8%.

[0083] Characterization of carbon materials Figure 1 The XRD pattern of bamboo precursor (a) shows a distinct diffraction peak at 2θ = 22.03°, corresponding to the (002) crystal plane of the ordered cellulose microfibrils in bamboo. The interplanar spacing is calculated to be 4.03 Å according to the Bragg equation. Figure 1Analysis of b (differential thermogravimetric curve of bamboo) shows that the main weight loss peak of bamboo pyrolysis corresponds to a temperature of 350 ℃, and the inflection point where the weight loss rate in the second stage tends to level off is at 500 ℃. Therefore, choosing 500 ℃ for low-temperature seeding and continuous induction of bamboo precursors can not only fully pyrolyze and remove hydrogen-containing, nitrogen-containing groups and most oxygen-containing groups, but also avoid the collapse of the ordered carbon skeleton of cellulose through the slow pyrolysis process induced by low temperature, promoting the combination of remaining oxygen-containing groups with carbon to form an ordered structure of oxygen-containing six-membered ring network, providing "oxygen-containing lattice memory anchor points" for the subsequent formation of ordered carbon sheet stacking structures with large interfacial spacing.

[0084] Figure 1 In the image, c represents the infrared spectrum of the bamboo precursor, which shows that it contains abundant -OH groups (3420 cm⁻¹). -1 CH (2870 / 2940 cm) -1 ), CN (1380 cm) -1 ), COC (1160 cm) -1 It contains hydrogen, nitrogen, and oxygen functional groups, etc. Figure 1 The d-curve I in Example 1 corresponds to the infrared spectrum of the bamboo-based subcrystalline carbon intermediate after induction at 500 ℃ for 2 h in step (2) and acid-base purification in step (4). Compared with the infrared characteristics of the precursor, the CH and CN peaks have basically disappeared, confirming the conclusion in the thermogravimetric analysis that "hydrogen-containing and nitrogen-containing groups have been fully removed"; at the same time, stable oxygen-containing functional groups such as COC are retained, which is consistent with the structural characteristics of "oxygen-containing lattice memory anchor points". The low temperature range of step (2) of this invention is limited to 400~600 ℃. The core basis is that 500 ℃ is the optimal temperature (as shown in Example 1), and 400 ℃ and 600 ℃ are reasonable extension ranges. Based on the pyrolysis kinetics, the bamboo-based subcrystalline carbon intermediate can still be obtained stably, and the structure will not be unstable due to temperature deviation.

[0085] Figure 1 Curve Ⅱ in the figure corresponds to bamboo-based subcrystalline carbon material: its characteristic absorption peaks for COC and CO completely disappear, indicating that the oxygen-containing six-membered ring network undergoes carbon-oxygen substitution and transforms into a carbon six-membered ring network; only a small amount of C=O remains (1630 cm⁻¹). -1 ) and -OH (3430 cm -1 The presence of functional groups (corresponding to a small amount of carboxyl groups, -COOH) indicates that the product has not been completely converted into perfect graphite-like crystalline carbon, confirming that the product of this invention is "graphite-like subcrystalline carbon".

[0086] Figure 2 In the figure, 'a' represents the transmission electron microscopy (TEM) characterization of bamboo-based subcrystalline carbon, showing that the carbon sheets in the material exhibit a highly consistent long-range orientation; its corresponding selected area electron diffraction (SAED)... Figure 2The illustration in Figure a shows a broadened and diffuse diffraction pattern (without the sharp, regular lattice of a single crystal, or the complete diffraction rings of a polycrystalline material or the diffuse halo rings of an amorphous material), corresponding to the subcrystalline structure's characteristic of "the interplanar spacing of nearly parallel carbon sheets being distributed within a certain range". Figure 2 The high-resolution TEM (HRTEM) results of bf show that the bamboo-based subcrystalline carbon is composed of stacked carbon sheets with nearly parallel long-range consistent orientations, and its (002) interplanar spacing is distributed between 3.71 and 4.0 Å, which is consistent with the diffraction results and is consistent with the characteristics of graphite-like subcrystalline structure.

[0087] Figure 3 In the figure, 'a' represents the XRD pattern of bamboo-based subcrystalline carbon: broadened envelope peaks corresponding to the (002) and (100) planes appear at positions 23.5° and 43.6°, respectively, instead of sharp diffraction peaks. This phenomenon originates from the macroscopic statistical detection principle of XRD, combined with the microstructural characteristics of the material: the interplanar spacing of graphite-like subcrystals in different regions within bamboo-based subcrystalline carbon fluctuates within a certain range (not completely uniform), causing the diffraction angles of each microcrystalline domain to continuously shift to meet the Bragg diffraction conditions, breaking the strict periodic lattice arrangement requirement for crystal diffraction, and the originally single diffraction peak is thus broadened into a continuous broadened envelope peak. This feature is consistent with the microstructure observed by TEM: the graphite-like subcrystals are incompletely developed and the interplanar spacing is non-uniform, and the corresponding SAED also shows broadened diffuse diffraction spots (rather than single crystal diffraction points). According to the Bragg equation, the interplanar spacing corresponding to the center of the (002) peak at 23.5° is 3.78 Å. This value is within the range of (002) interplanar spacing observed by TEM and is much larger than the (002) interplanar spacing of graphite crystals (3.37 Å). The peak height ratio (I) of the (002) peak to the (100) peak in Example 1 (manual grinding of the intermediate product after low-temperature induction for 10 min) is... (002) / I (100) The value was 3.13, significantly higher than that of bamboo-based carbon materials prepared by other grinding processes (see Table 1). Figure 3 The relationship between structural order and grinding process in the *be* section presents a "volcano-shaped curve." For example, based on manual grinding for 10 minutes (step 3), ball milling was performed for 2 hours (Example 2), 4 hours (Comparative Example 1), and 6 hours (Comparative Example 2), respectively. (002) / I (100) The I values ​​decreased sequentially to 2.67, 2.49, and 2.37; the I values ​​of the samples were manually ground for 5 minutes (Comparative Example 3). (002) / I (100)The value is 2.86. This indicates that the grinding process plays a crucial role in regulating the intermediate particle size and the microstructure of the induction stage: the intermediate particle size (57.1 μm) obtained under the grinding conditions of Example 1 is most conducive to the formation of long-range ordered stacked carbon sheets, thereby significantly improving the X-ray diffraction efficiency of the (002) crystal plane; conversely, excessive grinding (such as extending the ball milling time to 2-6 h) results in overly fine particles (13.6-4.2 μm), and the contact interface between particles will act like "resistance hinders current transmission", hindering the continuous transmission of the induction effect of the graphite crucible (seed crystal) between particles, resulting in insufficient crystallization induction at high temperature, which is not conducive to the ordered stacking of carbon sheets; while insufficient grinding (too short a time, such as manual grinding for 5 min) will result in overly large particles (62.1 μm), leading to insufficient internal carbon-oxygen replacement, and too many oxygen-containing functional groups are also not conducive to the formation of an ordered stacked structure of carbon sheets.

[0088] Figure 4 In Table 1, 'a' represents the X-ray photoelectron spectroscopy (XPS) full spectrum of Example 1, indicating that the main elements of bamboo-based subcrystalline carbon are carbon and oxygen (no other impurity elements were detected). As shown in Table 1, the oxygen content of the samples decreased with decreasing intermediate particle size: the oxygen content of the bamboo-based subcrystalline carbon in Example 1 was 10.7 at.%, significantly higher than that of bamboo-based derived carbon materials prepared by excessive grinding (such as Example 2 (6.28 at.%), Comparative Example 1 (5.53 at.%), and Comparative Example 2 (4.15 at.%)), but lower than that of bamboo-based derived carbon materials prepared by insufficient grinding (such as Comparative Example 3 (13.08 at.%)). Figure 4 bf in the image is a high-resolution C 1s XPS spectrum (where bf is the C 1s XPS spectrum). Figure 4 In this context, b corresponds to Example 1. Figure 4 The 'c' in the example corresponds to Example 2. Figure 4 The df values ​​in the diagram correspond to proportions 1-3 respectively. Figure 4 The hl values ​​in the diagram correspond to proportions 4-8 respectively. Peak fitting of the C 1s XPS spectra reveals binding energies at 284.8 eV, 285.8 eV, 286.5 eV, and 289.0 eV, corresponding to sp values ​​respectively. 2 Hybridized carbon (sp) 2 C), sp 3 Hybridized carbon (sp) 3 C), C O single bond, O=C O bond. Figure 4 g in the context is sp 2 C and sp 3 C peak area ratio (A) sp² / A sp³ ), which is related to I in XRD (002) / I (100)They all reflect structural order and exhibit completely consistent patterns of change: Example 1, A of bamboo-based subcrystalline carbon. sp² / A sp³ The value was 6.67, significantly higher than other grinding strength samples (see Table 1). Figure 4 (bf in the middle), corresponding to its highest XRD I. (002) / I (100) This confirms that its crystal structure has the best degree of order. Specifically, based on manual grinding for 10 minutes (step 3), it was ball-milled for 2 hours (Example 2), 4 hours (Comparative Example 1), and 6 hours (Comparative Example 2), respectively, and its A sp² / A sp³ The values ​​decreased sequentially to 5.10, 4.42, and 4.02; the A value of the sample was obtained by manual grinding for 5 min (Comparative Example 3). sp² / A sp³ It is 5.51, which is consistent with I in XRD. (002) / I (100) The trends are consistent, exhibiting a "volcano-shaped curve" pattern: the orderliness of the carbon sheet stacking / structure is the result of the synergistic effect of "sufficient carbon-oxygen substitution" and "graphite seed-induced continuity" corresponding to the intermediate particle size. The intermediate particle size in Example 1 is moderate, precisely achieving "sufficient but not excessive carbon-oxygen substitution" (preserving key oxygen-containing lattice memory to maintain parallel carbon sheets with large interlayer spacing) and "effective and continuous graphite induction" (avoiding interparticle interfaces hindering induction transfer, corresponding to high XRD Ig). (002) / I (100) This process ultimately forms a highly parallel, homogeneous carbon sheet structure. However, if the particles are excessively refined (e.g., by extending the ball milling time), although carbon-oxygen replacement is more complete (oxygen content decreases), the interparticle contact interface will block the inductive effect, similar to the "resistance hindering current transmission" in XRD analysis, leading to insufficient crystallization and causing A... sp² / A sp³ with I (002) / I (100) Simultaneous reduction; if grinding is insufficient (e.g., manual grinding for 5 minutes), carbon-oxygen replacement is inadequate (oxygen content is too high), resulting in excessive O=C. O-containing functional groups such as O can disrupt the ordered stacking of carbon sheets, corresponding to I in XRD. (002) / I (100) With XPS A sp² / A sp³ All were lower than in Example 1.

[0089] The TEM results of Comparative Example 2 (hand-grinding for 10 min followed by ball milling for 6 h) further confirm the effect of over-grinding: such as Figure 5In example a, the SAED spectrum shows a significantly broadened and diffused diffraction spot with the formation of small diffraction rings, indicating a further reduction in the long-range order of the carbon material. This aligns with the mechanism that "excessive particle refinement increases the contact points, hindering the induction of graphite seed transfer." Corresponding HRTEM observations reveal two key structural changes: first, the excessively small size of the intermediate particles hinders the induction of graphite seed transfer, significantly reducing the ordered stacking of carbon sheets and resulting in a distinct wavy morphology with significant bending at large scales; second, the excessively small size of the intermediate particles leads to excessive carbon-oxygen substitution reactions, resulting in excessive removal of oxygen-containing groups and a significantly narrowed (002) interplanar spacing compared to Example 1 (3.71~4.0 Å) to 3.61~3.73 Å. This wavy, bent carbon sheet and reduced interlayer spacing significantly increase the diffusion resistance of sodium ions.

[0090] Figure 3 fh and Figure 4 The hk values ​​represent the characterization results of bamboo-based derived carbon materials prepared in Comparative Examples 4-7 (designed based on the key process parameters of Example 1, differing only in the induction method and precursor / intermediate morphology). As shown in Table 1, compared with Example 1 (I... (002) / I (100) = 3.13、A sp² / A sp³ Compared to Example 1 (6.67), all three exhibit the common characteristic of "significantly lower structural order than Example 1": I (002) / I (100) The values ​​were 2.60 (Comparative Example 4), 2.33 (Comparative Example 5), and 2.75 (Comparative Example 6), respectively. sp² / A sp³ The values ​​were 4.91 (Comparative Example 4), 3.63 (Comparative Example 5), 3.80 (Comparative Example 6), and 4.90 (Comparative Example 7), respectively. This confirms the significant impact of deviations in key process parameters on the homogeneity and orderliness of carbon material structures, as detailed below: Comparative Example 4: The core process deviation from Example 1 is "no grinding after low-temperature induction (maintaining a continuous structure) + full-process twin seeding induction (graphite crucible + graphite powder)". Excessive continuous induction of twin seeds at the high-temperature stage accelerates the removal of oxygen-containing functional groups in local areas, leading to preferential nucleation of the graphite phase. Figure 3 The value of 2θ = 44.39° in f corresponds to the (101) plane diffraction peak of the graphite phase (XRD standard card: 41-1487) in the composite structure. (100)= 2.03 Å); meanwhile, the continuous structure, compared to the particulate morphology, resulted in insufficient internal carbon-oxygen substitution reaction (oxygen content of 13.86 at.% was significantly higher than in Example 1). The incompletely removed oxygen-containing functional groups interfered with the orderly stacking of carbon sheets, ultimately forming a graphite phase-disordered carbon composite structure with a significantly lower degree of structural order than in Example 1. This indicates that the synergistic effect of using a single crystal seed (graphite crucible) and intermediate product powder in the high-temperature stage is crucial. It is beneficial for the full carbon-oxygen substitution reaction, while in the double crystal seed, the graphite powder is difficult to completely separate from the final powder product, easily introducing impurities and interference, further highlighting the rationality of the single crystal seed design.

[0091] The core difference between Comparative Example 5 and Comparative Example 4 lies solely in the fact that "only single-crystal seeding with a graphite crucible was used throughout the entire process (no graphite powder was added as a second seed crystal)." All other process conditions (no grinding after low-temperature induction, maintaining a continuous structure) are completely identical (both differ from Example 1 in that they exhibit a "continuous morphology" process). Although its oxygen content (13.80 at.%) is close to that of Comparative Example 4 (13.86 at.%), indicating that the degree of carbon-oxygen substitution is comparable (carbon-oxygen substitution mainly occurs in the high-temperature stage, not in the low-temperature induction stage), but I (002) / I (100) = (2.33) and A sp² / A sp³ (3.63) is further reduced compared to Comparative Example 4, which fully demonstrates that the synergistic effect of the double seed crystals of graphite powder and graphite crucible is crucial in the low-temperature stage. The encapsulation and full contact of graphite powder with the bamboo-based continuum can enhance the induced continuity, enabling the oxygen-containing six-membered ring network to topologically replicate the original ordered arrangement of cellulose through the "oxygen-containing lattice memory" effect, avoiding insufficient driving force for ordering caused by single seed crystal induction, and laying the foundation for the directional growth of carbon skeleton in the high-temperature stage.

[0092] Comparative Example 6: The core difference from Example 1 is that a powdered bamboo-based precursor was used in the low-temperature stage (replacing the macroscopic continuum precursor), and single-crystal seeding was performed throughout (only a graphite crucible was used, without graphite powder synergy). Based on Table 1 and the characterization data, its structural order index (I... (002) / I (100) = 2.75, A sp² / A sp³ = 3.80) significantly lower than Example 1. The core reason for this result is that the powdered precursor is a dispersed particle, lacking the directional support of the fiber bundles in a macroscopic continuum. This makes it difficult for the graphite crucible to form a continuous directional guiding path, resulting in insufficient induction continuity and directionality. Consequently, it is impossible to topologically replicate the ordered structure of cellulose through the "oxygen-containing lattice memory effect" at low temperatures, ultimately leading to a decrease in the orderliness of the carbon sheet stacking. This further confirms that "the macroscopic continuum structure of the bamboo-based precursor at low temperatures is the key foundation for achieving full induction and ensuring structural orderliness."

[0093] The difference between Comparative Example 7 and Comparative Example 6 is that 5% graphite powder by mass of the powdered precursor was added and mixed evenly in Comparative Example 7. This is equivalent to using a double seed (graphite crucible + graphite powder) to induce the powdered precursor and intermediate throughout the entire process (high temperature + low temperature), while Comparative Example 6 uses a single seed to induce the powdered precursor and intermediate throughout the entire process. The difference from Example 1 is that Example 1 uses a double seed (graphite crucible + graphite powder) to induce the bamboo-based macroscopic continuous precursor in the low temperature stage, while using a single seed (graphite crucible) to induce the powdered precursor in the high temperature stage. (Refer to Table 1 and...) Figure 4 k in the comparison with the structural order index (A) in Example 7 sp² / A sp³ = 4.90) higher than Comparative Example 6 (A) sp² / A sp³ = 3.80) The reason is partly due to the increased induction intensity of the powdered precursor and intermediate in the twin seed, which makes the bamboo-based carbon product sp 2 The proportion of hybrid carbon increases; on the other hand, graphite itself is sp. 2 Hybrid carbon, which cannot be effectively separated from bamboo-based carbon products, also increases the sp... 2 The proportion of hybrid carbon. However, Comparative Example 7 is much lower than that of Example 1 (A). sp² / A sp³ = 6.67), which further verifies that "the macroscopic continuum structure of bamboo-based precursors in the low-temperature stage is the key foundation for achieving full induction and ensuring structural orderliness". The above comparative experiments further confirm the scientific validity and necessity of the process design of "low-temperature double seed + continuum to achieve full continuous induction" and "high-temperature single seed + powder to achieve carbon-oxygen replacement and lattice repair" in Example 1.

[0094] Figure 5 The dm in the diagram shows the TEM characterization results of the composite carbon material in Comparative Example 4. Its microstructure is mainly composed of the following four types: (1) Quasi-graphite crystals ( Figure 5 The df in the middle shows a structural feature between single crystal and polycrystalline. Its SAED pattern shows that the diffraction spots are discretely distributed and tend to be arranged along the diffraction rings (but no continuous diffraction rings are formed). Compared with the graphite subcrystal in Example 1, the carbon sheet stacks corresponding to the (002) plane and (100) plane are more parallel, and the interplanar spacing is narrowed to 3.70~3.77 Å ((002) plane) and 2.22~2.27 Å ((100) plane), respectively, which reflects a higher structural order. (2) Graphite phase ( Figure 5 g): Observed (100) crystal plane fringes at d = 2.03 Å, with Figure 3 The value of f in 2θ = 44.39° corresponds to the d of the (101) plane diffraction peak of the graphite phase.(100) = 2.03 Å consistent. The formation of graphite phase and quasi-graphite crystals is attributed to over-induction: graphite powder is in full contact with the intermediate products after low-temperature induction, which accelerates the removal of oxygen-containing functional groups, promotes the assembly of cracked carbon atoms into planar six-membered rings, and drives the preferential nucleation of graphite and quasi-graphite crystals. (3) Graphite subcrystals ( Figure 5 h, i in: consistent with the structure observed in Example 1. (4) Fractured and large-angle bent corrugated carbon sheet stack structure ( Figure 5 In the continuous intermediate, excessively long fibers are prone to thermal stress fracture and bending during pyrolysis, disrupting the internal induced continuity. Simultaneously, compared to the particulate intermediate, the carbon-oxygen substitution reaction in the continuous structure is insufficient, and excessive oxygen-containing functional groups further cause carbon sheet distortion, manifested as an expanded (002) interplanar spacing fluctuation range (3.64~4.07 Å), with the carbon sheets exhibiting a wavy, large-angle-bent, disordered stacking characteristic. The aforementioned fourth type of structural feature directly leads to the I in Comparative Example 4. (002) / I (100) With A sp² / A sp³ Significantly lower than Example 1.

[0095] Figure 6 Raman surface scan I of Example 1 (bamboo-based subcrystalline carbon) and Comparative Example 4 (bamboo-based composite carbon material) D / I G The ratio distribution diagram and representative spectra reveal differences in structural uniformity, which corroborate the TEM observation results (consistent with the correlation between Raman spectra and microstructure of carbon materials: I) D / I G The lower the ratio, the lower the sp. 2 The higher the orderliness of the carbon domains, the fewer the defects; the higher the ratio, the greater the structural disorder and the more defects. Figure 6 a (Scan of Example 1) and Figure 6 b (typical spectrum of Example 1) shows: I of bamboo-based subcrystalline carbon D / I G The area scan shows a uniform green distribution across the entire area, corresponding to I. D / I G The ratio range is 1.00-1.20; typical Raman spectra extracted from the area scan ( Figure 6 b) shows I D / I G = 1.14. This ratio and the uniformity of distribution indicate that bamboo-based subcrystalline carbon is composed of highly ordered, nearly parallel stacked carbon sheets, with no obvious structural defects or heterogeneous phases, and excellent structural homogeneity. Figure 6 c (comparative 4-sided scan) and Figure 6 The d-value (typical spectrum of Comparative Example 4) shows that: I of bamboo-based composite carbon materialD / I G The area scan shows a multi-regional differential distribution, except for large green areas (1.0 ≤ I). D / I G <1.20, corresponding to graphite subcrystalline carbon, with the same structure as in Example 1) In addition, there are three types of characteristic regions: blue region (I D / I G The <0.45 interval corresponds to the graphite phase (sp). 2 The carbon domain exhibits the highest long-range order and the fewest defects; the light blue region (0.45 ≤ I) D / I G The <1.0) interval corresponds to quasi-graphite crystals (with a slightly lower degree of order than graphite crystals, but higher than graphite sub-grains); the yellow region (1.20 ≤ I) D / I G <1.3): Corresponding to fracture, large-angle bending, corrugated carbon sheet stacking structure (increased structural disorder, edge defects and carbon sheet twisting lead to I D / I G (The ratio increased).

[0096] Figure 5 The HRTEM results of no in the sample show that Comparative Example 8 (bamboo-based hard carbon) is composed of randomly oriented, short, and curved graphene stacks in a disordered manner; the diffuse halo characteristics of SAED further confirm its amorphous structure. (See Table 1 for details.) Figure 3 i (XRD) and Figure 4 The high-resolution C 1s XPS spectra data show that the oxygen content of this bamboo-based hard carbon is as high as 15.3 at.% (the highest among all samples). (002) / I (100) Only 2.01, A sp² / A sp³ The value was only 2.64 (the lowest among all samples), confirming that its disordered layer structure significantly weakened the diffraction intensity of the (002) crystal plane.

[0097] Figure 7 In the figure, 'a' represents the N2 adsorption-desorption isotherm of the bamboo-based subcrystalline carbon material in Example 1. It exhibits a type III isotherm, showing non-porous characteristics and a specific surface area of ​​only 0.63 m². 2 g -1 The extremely small specific surface area can reduce side reactions with the electrolyte, which is one of the important factors in improving the first coulombic efficiency. Figure 7 In Figure 'b', the N2 adsorption-desorption isotherm of bamboo-based hard carbon (Comparative Example 8) is a type IV isotherm, exhibiting mesoporous characteristics and a specific surface area of ​​14.53 m². 2 g -1The disordered structure and mesoporous formation of hard carbon originate from the following core factors: bamboo precursors are mainly cellulose, and also contain lignin, hemicellulose, and abundant oxygen-containing functional groups; during direct pyrolysis without graphite seed induction, a large number of residual oxygen-containing functional groups will destroy sp. 2 The six-membered carbon ring structure hinders the orderly stacking of carbon sheets, and the cross-linking structure of lignin easily forms sp. 3 Carbon has an amorphous structure, while hemicellulose readily forms a porous structure; all three factors collectively interfere with sp. 2 The orderly growth of carbon networks. This result further confirms that graphite seed crystals are the core factor in improving the structural order of carbon materials. They can both accelerate the cracking of oxygen-containing groups to reduce oxygen content and promote the orderly assembly of carbon sheets through directional induction.

[0098] Based on the above characterization analysis and the influence of process parameters, the growth mechanism of graphite-like subcrystalline carbon can be systematically summarized into the following three points, with precise structural control achieved throughout the process through process synergy: (1) Low-temperature twin seeding continuous induction (laying the foundation for ordered carbon in bamboo-based subcrystalline structures): Maintaining the macroscopic continuous structure of the bamboo-based precursor, the synergistic effect of graphite crucible + graphite powder twin seeding is utilized to fully induce the formation of ordered six-membered carbon rings by fully cleaving hydrogen- and nitrogen-containing groups, thereby reducing the Gibbs free energy of disordered components such as lignin, hemicellulose, and oxygen-containing functional groups. This induces the formation of a continuous oxygen-containing six-membered ring network. This network inherits the ordered structure characteristics of cellulose with large interlayer spacing through the "oxygen-containing lattice memory effect," avoiding the induction of discontinuous disordered structures and providing an ordered template for subsequent subcrystalline growth.

[0099] (2) High-temperature single crystal seed + powdered intermediate to achieve carbon-oxygen substitution (precise structure control): The intermediate product is ground into powder (exposing more reaction surface and shortening atomic diffusion path), and a graphite crucible is used as a single crystal seed to avoid over-induction and ensure carbon-oxygen substitution efficiency. At high temperature, oxygen-containing groups are removed to achieve full in-situ carbon-oxygen substitution. Carbon atoms fill oxygen vacancies to achieve lattice repair, thereby promoting the directional growth of carbon six-membered ring network. At the same time, the single crystal seed "insufficiently induces" the nucleation of graphite phase, the powder morphology ensures the appropriate carbon-oxygen substitution, and the internal fibers of the particles are not easy to break, which can provide continuous induction and avoid the generation of disordered structure.

[0100] (3) Synergistic effect to form target structure: The "low temperature continuum + double seed" ensures the induced continuity and oxygen-containing lattice memory, while the "high temperature single seed + powdered intermediate" balances the oxygen-containing group cracking efficiency and carbon-oxygen replacement appropriateness, and simultaneously achieves lattice repair. Finally, the target product of homogeneous single bamboo-based subcrystalline carbon with a large interlayer spacing of 3.71~4.0 Å is formed by long-range stacked near-parallel carbon sheets.

[0101] Electrochemical performance characterization analysis The electrochemical performance and physicochemical properties of Examples 1-5 and Comparative Examples 1-9 are summarized in Table 1 below: Table 1. Comparison of physicochemical properties and electrochemical performance of the examples and comparative samples.

[0102] Figure 8 The ae curves in Table 1 represent the initial discharge-charge curves of Examples 1 and 2, and Comparative Examples 1-3. (This is in conjunction with the data in Table 1.) Figure 8 Analysis of the comparison charts of the initial charge specific capacity and initial coulombic efficiency in fg shows that the evolution of intermediate particle size in Examples 1, 2 and Comparative Examples 1-3 significantly affects the material structural order (I). (002) / I (100) A sp² / A sp³ Both the electrochemical performance and the structure exhibit a clear "volcano-shaped curve" pattern. As the intermediate particles become finer due to excessive grinding (Example 2, Comparative Example 1, Comparative Example 2), the structural order gradually decreases, leading to a synchronous decrease in the specific capacity during the first charge. Figure 8 The bd values ​​ranged from 342.0 to 331.9 to 326.1 mAh / g. However, the initial coulombic efficiency exhibited a significant initial decrease followed by a plateau: it dropped significantly from 94.4% in Example 1 to approximately 90% (Example 2, 90.2%) and then stabilized, without decreasing further with decreasing particle size (Comparative Example 1, 90.1%; Comparative Example 2, 90.3%). This phenomenon stems from the dual effect of "structural order-surface chemistry" induced by particle refinement: on the one hand, reduced structural order weakens the reversibility of sodium ion intercalation / deintercalation (negative effect); on the other hand, excessive carbon-oxygen substitution significantly reduces the content of oxygen-containing functional groups in the material (see Table 1), which helps reduce the irreversible adsorption of sodium ions by oxygen-containing groups (positive effect). These two effects balance each other, resulting in the initial coulombic efficiency remaining within a narrow range of 90.1%-90.3% in the excessively refined particle range. Furthermore, the excessively large particles in Comparative Example 3 (insufficient grinding) also resulted in insufficient internal carbon-oxygen replacement, leading to a lower structural order than Example 1. Its initial charge specific capacity was 332.3 mAh / g, and its initial coulombic efficiency was 91.6%. Figure 8 The (e) further confirms the core principle that "moderate intermediate particle size is the key to ensuring optimal structural order and electrochemical performance".

[0103] Figure 8Table 1 shows the initial discharge-charge curves of carbon materials prepared due to improper induction methods or inappropriate precursor / intermediate morphology (Comparative Examples 4-7). As shown in Table 1, these samples all exhibited synchronously deteriorating electrochemical performance due to low structural order, with their initial charge specific capacity and efficiency significantly lower than those of Example 1: the initial charge specific capacity and initial coulombic efficiency were 324.5 mAh / g (89.5%, Comparative Example 4), 307.0 mAh / g (89.0%, Comparative Example 5), 316.4 mAh / g (89.7%, Comparative Example 6), and 309.1 mAh / g (92.4%, Comparative Example 7), respectively. This confirms the correlation between deviations in induction process parameters and "structural order-electrochemical performance." In particular, Comparative Example 4, besides the decrease in structural order caused by fractured, large-angle-bent corrugated carbon sheets, which hinders sodium ion diffusion and increases irreversible intercalation / deintercalation, differs most significantly from other comparative examples in that it generates a graphite phase without sodium storage activity. This additional structural defect also leads to a decrease in its charging capacity and initial coulombic efficiency. Comparative Example 6 uses a closed graphite container with a single crystal seed to induce the powder throughout the process, but its initial charging specific capacity and initial coulombic efficiency are significantly lower than Example 1. The core reason is that Example 1 of this invention employs a dual-seed induction design for a macroscopically continuous precursor at low temperatures, which can more completely replicate the ordered structure of cellulose through sufficient continuous induction and the "oxygen-containing lattice memory effect." This unique induction mechanism results in superior carbon structural order, specifically manifested in the I... (002) / I (100)The efficiency of the first charge was significantly higher than that of Comparative Example 6 (Example 1: 3.13; Comparative Example 6: 2.75), and its Asp² / Asp³ ratio was also higher (Example 1: 6.67; Comparative Example 6: 3.80). These structural parameters fully demonstrate that Comparative Example 6, due to insufficient induced continuity and directionality, had a lower degree of order in the carbon sheet stacking, making it difficult to form the homogeneous graphite-like subcrystalline carbon structure composed of nearly parallel and uniformly oriented carbon sheet stacks protected by this invention. The first coulombic efficiency of Comparative Example 7 (92.4%) was better than that of Comparative Example 6 (89.7%), reflecting the "advantage of dual-seed synergistic induction to improve the order of carbon sheet stacking". However, the first charge specific capacity of Comparative Example 7 (309.1 mAh / g) was lower than that of Comparative Example 6 (316.4 mAh / g), mainly because the added graphite powder seed crystals could not be separated from the generated carbon-based material, diluting the specific capacity of the final carbon-based material product. The initial charge specific capacity and initial coulombic efficiency of Comparative Example 7 were both lower than those of Example 1 (353.5 mAh / g, 94.4%), indicating that although a dual-seed system was used in the low-temperature stage, the inherent limitations of the powdered precursor particles made it difficult to form a long-range continuous and directional guiding path for the induction of dual seeds in the stage where most organic groups were fully decomposed at low temperatures. In contrast, Example 1 used "low-temperature dual seeds + macroscopic continuous bamboo fiber bundles", and this continuous structure is the key carrier for the topological replication of the ordered arrangement of cellulose by the "oxygen-containing lattice memory effect". At high-temperature stage, only a single seed is needed to complete carbon-oxygen replacement and lattice repair - which is the core advantage of the "staged seeding + structure matching" process design of this invention.

[0104] Figure 8 In Figure 1, l represents the first discharge-charge curve of the hard carbon sample (Comparative Example 8). Its first charge specific capacity was 298.8 mAh / g, and its first coulombic efficiency was 86.3%, both significantly lower than those of the sample induced by graphite seeding. This indicates that graphite seeding can effectively reduce disordered carbon sheet stacking and structural defects, which is crucial for improving electrochemical performance.

[0105] It is worth noting that the capacity percentage of the low-voltage plateau (~0.1 V) corresponding to interlayer sodium removal behavior in the first charge curve of a half-cell is directly related to the potential for improving the energy density of the full cell: the subcrystalline carbon in Example 1, with its nearly parallel stacked carbon sheets with large interlayer spacing, facilitates reversible sodium removal, and its low-voltage plateau capacity percentage in the first charge curve reaches 81.7% (calculated using the tangent method of the first charge curve); while in Comparative Example 8, due to the disordered stacking of carbon sheets, the reversibility of interlayer sodium removal is reduced, and the corresponding low-voltage plateau capacity percentage is only 73.9% (same as the above tangent method).

[0106] The experimental data consistently demonstrate that the structural order of the carbon sheet stacks is crucial in determining the sodium ion intercalation / deintercalation kinetics and reversibility. The homogeneous graphite-like subcrystalline structure obtained in this invention, with its nearly parallel stacked carbon sheets and large interlayer spacing, achieves efficient and reversible sodium storage similar to graphite lithium storage. This is the fundamental reason why the material achieves high initial coulombic efficiency, high initial charge specific capacity, and excellent low-voltage plateau capacity.

[0107] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A bamboo-based, large-interlayer-spacing, homogeneous graphite-like subcrystalline carbon material, characterized in that, The phase of the bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing is graphite-like subcrystalline carbon; its structure is a homogeneous structure composed of nearly parallel carbon sheets with consistent long-range orientation; the interplanar spacing d of its (002) plane is... 002 The range is 3.71–4.0 Å.

2. The method for preparing the bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing as described in claim 1, characterized in that, Includes the following steps: Bamboo material was placed in a sealed graphite container filled with graphite powder, and the first induced growth reaction was carried out to obtain bamboo-based subcrystalline carbon intermediate. The bamboo-based subcrystalline carbon intermediate product was pulverized to obtain powdered bamboo-based subcrystalline carbon intermediate product. Impurities in the bamboo-based subcrystalline carbon intermediate were removed to obtain purified powdered bamboo-based subcrystalline carbon intermediate. The purified powdered bamboo-based subcrystalline carbon intermediate was placed in a sealed graphite container and subjected to a second induced growth reaction to obtain the bamboo-based homogeneous graphite subcrystalline carbon material with large interlayer spacing.

3. The method for preparing bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing according to claim 2, characterized in that, The reaction conditions for the first induced growth reaction include at least one of the following: a) The reaction temperature is 400-600℃; b) The heat preservation time is 1-3 hours; c) Heat to the reaction temperature at a heating rate of 0.5~5 ℃ / min; d) The reaction is carried out under a protective atmosphere.

4. The method for preparing bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing according to claim 2, characterized in that, The reaction conditions for the second induced growth reaction include at least one of the following: A) The reaction temperature is 1400-1600℃; B) The heat preservation time is 2-4 hours; C) Heat to the reaction temperature at a heating rate of 0.5~5 ℃ / min; D) The reaction is carried out under a protective atmosphere.

5. The method for preparing bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing according to claim 2, characterized in that, The particle size of the powdered bamboo-based subcrystalline carbon intermediate is 10~60 μm.

6. The method for preparing bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing according to claim 2, characterized in that, Specifically, the steps include: soaking the powdered bamboo-based subcrystalline carbon intermediate product in acid and / or alkali to remove impurities from the powdered bamboo-based subcrystalline carbon intermediate product.

7. The method for preparing bamboo-based homogeneous graphite-like subcrystalline carbon material with large interlayer spacing according to claim 2, characterized in that, The sealed graphite container includes one of a graphite crucible and a graphite boat; And / or, the graphite powder has a particle size of 0.3-0.8 μm.

8. The application of the bamboo-based homogeneous graphite subcrystalline carbon material with large interlayer spacing as described in claim 1 in battery active materials.

9. A battery negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector, wherein the negative electrode active layer includes the bamboo-based homogeneous graphite subcrystalline carbon material with large interlayer spacing as described in claim 1.

10. A sodium-ion battery, characterized in that, Includes the battery negative electrode sheet as described in claim 9.

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