Bamboo-based derived nitrogen-doped hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention discloses a bamboo-based derived nitrogen-doped hard carbon negative electrode material and a preparation method and application thereof.The preparation method creatively utilizes the characteristic that bamboo wood is rich in natural phenolic hydroxyl groups and comprises the steps that bamboo powder and an aldehyde group compound are subjected to in-situ phenol-aldehyde polycondensation under the alkaline condition, and a cross-linked network precursor is constructed; then adjusting the pH to weak acidity, and carrying out in-situ amination doping with a nitrogen-containing compound; and finally, carbonizing to obtain the nitrogen-doped hard carbon material. According to the method, structural reconstruction and uniform nitrogen doping of the bamboo-based precursor are synchronously realized through two-step continuous molecular-level reaction of'alkaline polycondensation-acidic amination '. When the obtained material is used as a sodium ion battery negative electrode, high reversible specific capacity (greater than 304 mAh / g), high first coulombic efficiency (greater than 92%) and excellent cycling stability (300-week capacity retention rate at 0.5 C is greater than 92%) are shown. The method is simple in process, green, low in cost and suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, specifically relating to a bamboo-based derived nitrogen-doped hard carbon anode material, its preparation method, and its application. Background Technology

[0002] With the advancement of the "dual carbon" strategy, sodium-ion batteries, as a key technology for large-scale energy storage, have seen the development of low-cost, high-performance anode materials become a research focus. Hard carbon materials are considered one of the most promising anode materials for sodium-ion batteries due to their abundant resources, low cost, and suitable sodium-ion storage platform capacity.

[0003] Biomass, especially bamboo, which is abundant and grows rapidly, is often used as a precursor for the preparation of hard carbon due to its natural porous structure and rich carbon source. However, hard carbon obtained by direct carbonization of natural bamboo has inherent defects such as disordered structure, uneven interlayer spacing, and insufficient active sites, which makes it difficult for its reversible specific capacity, initial coulombic efficiency, and long-term cycling stability to meet the requirements of commercial applications. To improve the performance of biomass hard carbon, existing technologies mainly focus on the following routes: (1) Pretreatment purification route, which removes inorganic components and impurities from biomass through acid washing, alkali dissolution, deashing and other means (such as Chinese patents with publication numbers CN118851149A and CN117658107A). Although this type of method can improve the purity of the material, it fails to fundamentally change the disordered carbon skeleton structure of biomass itself, and the performance improvement is limited; (2) Physical, biological or rapid pyrolysis means of structure regulation route, such as Chinese patents with publication numbers CN118529710A and CN117923462A, etc., to regulate the physical structure of the precursor in order to optimize the pores after carbonization. This type of method has a certain promoting effect on pore formation, but the regulation precision is limited and it cannot introduce heteroatom active sites at the molecular level.

[0004] The common bottlenecks in existing technologies are: (1) failure to effectively utilize the intrinsic chemical activity of biomass precursors for molecular-level structure design. For example, bamboo contains abundant natural polyphenols such as lignin and tannins, which theoretically can provide a large number of phenolic hydroxyl active sites, but existing methods have failed to actively and effectively utilize this chemical property to achieve directional reconstruction of the carbon skeleton. (2) Heteroatom doping strategies are mostly physical mixing or post-processing, with low doping efficiency and poor uniformity, making it difficult to form a stable and synergistic effect with the carbon matrix. (3) Process routes are often cumbersome, demanding, or require expensive reagents, making it difficult to meet the requirements of high performance, low cost, and green manufacturing. Therefore, developing a simple method that can fully utilize the chemical properties of biomass and simultaneously achieve precursor structure reconstruction and uniform heteroatom doping under mild conditions is of great significance for breaking through the performance bottleneck of biomass hard carbon and promoting its industrial application. Summary of the Invention

[0005] The purpose of this invention is to provide a bamboo-based derived nitrogen-doped hard carbon anode material, its preparation method, and its application, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a bamboo-based derived nitrogen-doped hard carbon anode material includes the following steps:

[0008] S1: Crush, wash and dry the bamboo raw material to obtain pretreated bamboo powder;

[0009] S2: Disperse the pretreated bamboo powder in an alkaline aqueous solution with a pH of 10-14, add an aldehyde-containing compound, and carry out an in-situ phenol-aldehyde condensation reaction at 60-90°C for 2-12 hours.

[0010] S3: Adjust the pH of the system obtained in step S2 to 4.0-6.5, add a nitrogen-containing compound, and carry out an in-situ amination doping reaction at 50-80℃ for 2-8 hours.

[0011] S4: The product after the reaction in step S3 is subjected to solid-liquid separation, washing, and drying, and then subjected to high-temperature carbonization treatment at 1000-1600℃ under an inert atmosphere to obtain the bamboo-based derived nitrogen-doped hard carbon anode material.

[0012] As a further aspect of the present invention: the aldehyde-containing compound in S2 includes at least one of formaldehyde, trioxymethylene, paraoxymethylene, glutaraldehyde, and glyoxal.

[0013] As a further aspect of the present invention: the nitrogen-containing compound in S3 includes at least one of urea, melamine, ammonia, ethylenediamine, and ethanolamine.

[0014] As a further aspect of the present invention: the high-temperature carbonization treatment in S3 is carried out at a temperature of 1300-1600℃, the heating rate is 2-5℃ / min, and the holding time at this temperature is 4-7 hours.

[0015] As a further aspect of the present invention: the final temperature of the high-temperature carbonization treatment in S3 is 1600℃, the heating rate is 3℃ / min, and the holding time is 5 hours.

[0016] As a further aspect of the present invention: it includes a current collector and a negative electrode material layer coated on the current collector, wherein the negative electrode material layer comprises the bamboo-based derived nitrogen-doped hard carbon negative electrode material.

[0017] As a further aspect of the present invention: the application of a bamboo-based derived nitrogen-doped hard carbon anode material as a sodium-ion battery anode.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. Innovative Principles and Utilization of Intrinsic Chemical Properties: This paper proposes and utilizes the characteristic of bamboo being rich in natural phenolic hydroxyl groups as the active starting point for controllable chemical reactions. Through the classic "phenol-aldehyde condensation" reaction, the molecular structure of biomass precursors is reshaped, transforming disordered biomass carbon sources into resin-like polymers with designable structures. This fundamentally improves the uniformity and controllability of the final carbon material structure.

[0020] 2. Achieved efficient and uniform in-situ doping: An innovative "base-first, acid-later" sequence is adopted, first constructing a robust cross-linked network framework, followed by an amination reaction under weakly acidic conditions. This strategy enables nitrogen-containing groups to chemically react with active sites on the framework (such as residual aldehyde and hydroxyl groups), achieving atomically uniform, in-situ doping of nitrogen with strong doping bonding and good high-temperature stability.

[0021] 3. The synergistic effect of the "structure-component" dual composite: After carbonization, the cross-linked network facilitates the formation of a well-defined, moderately defective hard carbon structure, providing a stable sodium ion storage framework and rapid ion diffusion channels. The uniformly distributed nitrogen doping not only significantly improves the electronic conductivity of the material but also introduces a large number of surface active sites and pseudocapacitive contributions, jointly enhancing the sodium storage capacity and reaction kinetics of the material. The synergy of these two factors results in excellent overall performance of the material, exhibiting high specific capacity (reversible capacity up to 304 mAh g⁻¹), high first-cycle efficiency (>92%), and excellent cycling stability (capacity retention >92% after 300 cycles).

[0022] 4. The process is green, simple, and cost-effective: The entire process is carried out in an aqueous phase under mild reaction conditions, requiring no complex equipment or expensive reagents. Using inexpensive bamboo as the sole carbon source, deep modification is achieved through a simple two-step liquid-phase reaction. The process is short, generates little waste, and has great potential for large-scale industrial production. Attached Figure Description

[0023] Figure 1 The scanning electron microscope (SEM) image of the bamboo-based nitrogen-doped hard carbon material (NC-HC-1600) prepared in Example 1 of this invention shows a lamellar morphology.

[0024] Figure 2 A comparison of the first charge-discharge curves of sodium-ion batteries assembled using materials from Example 1 (NC-HC-1600) and Comparative Example 1 (C-1600) as negative electrodes at a rate of 0.1C.

[0025] Figure 3Comparison of long-cycle performance at 0.5C rate for sodium-ion batteries assembled using the materials of Example 1 (NC-HC-1600), Example 2 (NC-HC-1400), Example 3 (NC-HC-GA), and Comparative Example 1 (C-1600) as negative electrodes. Detailed Implementation

[0026] 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 some embodiments of the present invention, and not all embodiments. 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.

[0027] Example 1

[0028] (1) Pretreatment of bamboo-based materials: Cut bamboo into sections, crush them mechanically, and pass them through a 100-mesh sieve to obtain bamboo powder. Wash the bamboo powder repeatedly with deionized water three times, and dry it in an 80℃ forced-air drying oven for 12 hours for later use.

[0029] (2) In-situ phenol-aldehyde polycondensation reaction under alkaline conditions: Weigh 10.0 g of the above-mentioned dried bamboo powder and disperse it in 200 mL of 1 mol / L sodium hydroxide aqueous solution (pH≈13), and stir to form a uniform suspension. Transfer the suspension to a three-necked flask equipped with a reflux condenser, heat it in a water bath to 45°C and keep it at a constant temperature. Then, slowly add 20 mL of 37% formaldehyde aqueous solution (as the aldehyde compound) dropwise with stirring. After the addition is complete, raise the temperature to 75°C and keep stirring at a constant temperature for 3 hours. After the reaction is completed, a brownish-brown viscous slurry is obtained.

[0030] (3) Acidic in-situ amination doping: The slurry obtained in step S2 was cooled to room temperature, and the pH of the system was slowly adjusted to 5.5 with dilute hydrochloric acid (1 mol / L) while stirring. Then, 5.0 g of urea (as a nitrogen-containing compound) was added, and the reaction was stirred in a water bath at 60°C for 4 hours.

[0031] (4) Pyrolysis and carbonization: The mixture after the reaction in step S3 was filtered and washed with deionized water until the filtrate was neutral. The resulting solid was dried overnight in an oven at 100°C. The dried precursor was placed in a tube furnace and carbonized at high temperature under the protection of continuously flowing high-purity nitrogen (flow rate 200 ml / min). The calcination procedure was as follows: the temperature was increased to 1600°C at a heating rate of 3°C / min and held at this temperature for 5 hours, followed by natural cooling to room temperature. The black blocky product after calcination was ground and passed through a 300-mesh sieve to obtain the final product—nitrogen-doped bamboo-based hard carbon material (labeled as NC-HC-1600).

[0032] Example 2

[0033] The only difference between this embodiment and Embodiment 1 is the carbonization temperature in step S4: the final carbonization temperature is set to 1400℃, while the other steps and parameters are exactly the same. The resulting product is denoted as NC-HC-1400.

[0034] Example 3

[0035] The only difference between this embodiment and Example 1 is the aldehyde compound in step S2: an equimolar amount of glutaraldehyde aqueous solution is used instead of formaldehyde aqueous solution; all other steps and parameters are exactly the same. The resulting product is denoted as NC-HC-GA.

[0036] Comparative Example 1 (Direct Carbonization)

[0037] 10.0 g of bamboo powder pretreated in step S1 of Example 1 was placed directly into a tube furnace without any chemical modification and carbonized under the same nitrogen atmosphere and heating program as in Example 1 (heating to 1600℃ at 3℃ / min and holding for 5 hours). The resulting product was designated C-1600.

[0038] Comparative Example 2 (Physical mixed doping, simulating existing technology)

[0039] Take 10.0 g of bamboo powder pretreated in step S1 of Example 1, and mix it thoroughly with 5.0 g of urea in a mortar and grind for 30 minutes. Place the mixture in a tube furnace and carbonize it under the same nitrogen atmosphere and temperature program as in Example 1. The resulting product is designated MC-1600.

[0040] Performance testing and characterization

[0041] Structure and morphology characterization: The product NC-HC-1600 obtained in Example 1 was subjected to scanning electron microscopy (SEM) analysis, and the results are as follows: Figure 1 As shown, the material exhibits a clear and well-developed lamellar structure, which is beneficial for electrolyte wetting and ion transport.

[0042] Electrochemical performance testing: The materials obtained in each example and comparative example were used as active materials, mixed with conductive carbon black and sodium carboxymethyl cellulose (CMC) binder in deionized water at a mass ratio of 8:1:1 to form a slurry, which was then uniformly coated onto copper foil. After drying, rolling, and stamping, a negative electrode sheet was formed. A sodium metal sheet was used as the counter electrode, a glass fiber membrane as the separator, and 1 mol / L NaPF6 (solvent EC:DEC = 1:1 volume ratio, containing 5% FEC) as the electrolyte. CR2016 button batteries were assembled in an argon glove box. Charge-discharge tests were performed using a Blue Battery testing system. The electrochemical performance test results are shown in Table 1.

[0043]

[0044] The above experimental results show that the synergistic modification method of "phenol-aldehyde polycondensation-amine doping" provided by this invention, especially the NC-HC-1600 prepared at 1600℃, has the best comprehensive performance, with high reversible capacity, high first efficiency and excellent cycle stability.

[0045] Comparative Example 1 (direct carbonization) had the worst initial performance and cycle performance, indicating that unmodified bamboo-derived hard carbon has serious defects.

[0046] Key Comparison: While Comparative Example 2 (physical mixing and doping) outperformed Comparative Example 1, it was still significantly inferior to Example 1 of this invention. This strongly demonstrates the synergistic effect of the two-step in-situ chemical reaction of "basic polycondensation-acidic amination" proposed in this invention (first constructing a stable cross-linked network, then achieving chemical bonding doping), the effect of which is far superior to that of simple "physical mixing + carbonization." This comparative data is key evidence of the non-obviousness and outstanding substantive features of this invention.

[0047] It should be noted that the above embodiments are merely preferred embodiments of the present invention, used to specifically illustrate the technical solution of the present invention and the excellent effects that can be achieved. The core of the present invention lies in providing a general methodology for "molecular-level structural reconstruction and uniform doping of biomass precursors rich in natural phenolic hydroxyl groups through a two-step continuous liquid-phase reaction of alkaline phenol-aldehyde condensation and acidic amination".

[0048] Those skilled in the art will understand that any biomass raw material rich in natural phenolic hydroxyl groups (especially those derived from lignin, tannins, etc.) can serve as a precursor for implementing the principles of this invention. Examples include, but are not limited to, other wood processing residues (such as pine sawdust, fir sawdust), agricultural waste (such as wheat straw, rice husks, corn cobs), and fruit shells (such as walnut shells, coconut shells). Employing the strategy of "first constructing a cross-linked network, then in-situ chemical doping" described in this invention also holds promise for effectively improving the structure and performance of its derived carbon materials. Given the differences in the specific components of different raw materials (such as the ratio of cellulose, hemicellulose, and lignin), those skilled in the art can adaptively optimize process parameters such as reaction solution concentration, pH value, temperature, and time through limited conventional experiments. This falls within the scope of conventional technical adjustments based on the core principles disclosed in this invention.

[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0050] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a bamboo-based derivative nitrogen-doped hard carbon negative electrode material, characterized in that, The method comprises the following steps: S1: crushing, washing and drying bamboo raw materials to obtain pretreated bamboo powder; S2: dispersing the pretreated bamboo powder in an alkaline aqueous solution with a pH value of 10-14, adding an aldehyde group-containing compound, and performing in-situ phenol-aldehyde polycondensation at 60-90℃ for 2-12 hours; S3: adjusting the pH value of the system obtained in step S2 to 4.0-6.5, adding a nitrogen-containing compound, and performing in-situ amine doping at 50-80℃ for 2-8 hours; S4: performing solid-liquid separation, washing and drying on the product after step S3, and then performing high-temperature carbonization treatment at 1000-1600℃ under the protection of an inert atmosphere to obtain the bamboo-derived nitrogen-doped hard carbon negative electrode material.

2. The method of claim 1, wherein the bamboo-based, nitrogen-doped hard carbon negative electrode material is prepared by the following steps: (1) preparing a bamboo-based carbon precursor; (2) mixing the bamboo-based carbon precursor with a nitrogen source; (3) heating the mixture to obtain a bamboo-based, nitrogen-doped hard carbon negative electrode material. The aldehyde group-containing compound in S2 at least contains one of formaldehyde, trioxane, polyoxymethylene, glutaraldehyde and glyoxal.

3. The method of claim 1, wherein the bamboo-based, nitrogen-doped hard carbon negative electrode material is prepared by the following steps: (1) preparing a bamboo-based carbon precursor; (2) mixing the bamboo-based carbon precursor with a nitrogen source; (3) heating the mixture to obtain a bamboo-based, nitrogen-doped hard carbon negative electrode material. The nitrogen-containing compound in S3 at least contains one of urea, melamine, ammonia, ethylenediamine and ethanolamine.

4. The method of claim 1, wherein the bamboo-based, nitrogen-doped hard carbon negative electrode material is prepared by the following steps: (1) preparing a bamboo-based carbon precursor; (2) mixing the bamboo-based carbon precursor with a nitrogen source; (3) heating the mixture to obtain a bamboo-based, nitrogen-doped hard carbon negative electrode material. The high-temperature carbonization treatment in S3 has a temperature of 1300-1600℃, a heating rate of 2-5℃ / min, and a holding time at the temperature of 4-7 hours.

5. The method of claim 1, wherein the bamboo-based, nitrogen-doped hard carbon negative electrode material is prepared by the following steps: (1) preparing a bamboo-based carbon precursor; (2) mixing the bamboo-based carbon precursor with a nitrogen source; (3) heating the mixture to obtain a bamboo-based, nitrogen-doped hard carbon negative electrode material. The high-temperature carbonization treatment in S3 has a final temperature of 1600℃, a heating rate of 3℃ / min, and a holding time of 5 hours. 6.A bamboo-based derivative nitrogen-doped hard carbon negative electrode material, characterized in that, It is obtained by the preparation method of any one of claims 1 to 5.

7. The use of a bamboo-based derivative nitrogen-doped hard carbon negative electrode material according to claim 6, characterized in that, The negative electrode material layer comprises the bamboo-derived nitrogen-doped hard carbon negative electrode material of claim 6.

8. Use of the bamboo-derived nitrogen-doped hard carbon negative electrode material of claim 1 as a negative electrode of a sodium ion battery.

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