Biomass-based carbon negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of negative electrode materials, in particular to a biomass-based carbon negative electrode material and a preparation method thereof.The negative electrode material is prepared from, by weight, 50-70 parts of nitrogen and phosphorus co-doped bamboo charcoal, 25-40 parts of zinc modified phenolic resin and 5-10 parts of asphalt, the nitrogen and phosphorus co-doped bamboo charcoal contains, by mass, 1.5-3.5% of nitrogen, 0.5-2.0% of phosphorus, and the balance zinc modified phenolic resin; the zinc element exists in the form of a ZnO or Zn-Nx-C coordination structure, and the mass fraction is 0.1-1.0%. According to the biomass-based carbon negative electrode material and the preparation method thereof, the prepared negative electrode material has high reversible capacity, high first coulombic efficiency, excellent rate capability and long cycle stability.

Description

Technical Field

[0001] This invention relates to the field of anode material technology, and in particular to a biomass-based carbon anode material and its preparation method. Background Technology

[0002] Sodium-ion batteries are favored because sodium resources are abundant (2.36% in the Earth's crust, far exceeding lithium's 0.0065%) and inexpensive (raw material costs are only 1% of those of lithium-ion batteries). 3-1 2) With its environmentally friendly nature and lack of resource and geographical risks, sodium-ion battery storage exhibits irreplaceable application prospects in low-speed electric vehicles, base station energy storage, and residential energy storage, making it one of the current research hotspots in the field of electrochemical energy storage. The anode material, as a core component of sodium-ion batteries, directly determines the battery's capacity, initial coulombic efficiency, rate performance, and cycle stability. Currently researched anode materials for sodium-ion batteries mainly include carbon-based materials, alloy materials, and metal compound materials. Among these, carbon-based materials are the most industrially promising type due to their good conductivity, structural stability, and controllable cost. Hard carbon materials, with their disordered carbon structure, adjustable interlayer spacing, and abundant porosity, can adapt to the insertion / desorption requirements of sodium ions (ionic radius 0.102 nm) and are considered an ideal choice for sodium-ion battery anode materials.

[0003] However, existing hard carbon anode materials, especially biomass-based hard carbon materials, still face three major technological bottlenecks in practical applications: (1) Existing technologies for modifying biomass hard carbon are mostly focused on single elements (such as only nitrogen doping or phosphorus doping) or single processes (such as only carbonization temperature adjustment), making it difficult to achieve synergistic optimization of multiple performance dimensions. (2) In the traditional preparation process of biomass hard carbon, the carbonization process mostly adopts a crude control of a single heating rate and a fixed final temperature, which cannot achieve systematic control of interlayer spacing, pore type and closed pore content. (3) Some high-performance hard carbon materials rely on expensive precursors (such as resin-based and polymer-based raw materials) or complex preparation processes (such as template method and atomic layer deposition method), resulting in high production costs; while biomass hard carbon with agricultural and forestry waste (such as bamboo, wood and straw) as precursors has low raw material costs, but due to high ash content (>5%) and poor structural uniformity, it requires multiple complex purification processes, making it difficult to achieve large-scale production and restricting its industrial application. Summary of the Invention

[0004] The purpose of this invention is to provide a biomass-based carbon anode material and its preparation method. The anode material obtained has high reversible capacity, high initial coulombic efficiency, excellent rate performance and long cycle stability.

[0005] To achieve the above objectives, this invention provides a biomass-based carbon anode material. The anode material comprises, by weight, 50-70 parts of nitrogen-phosphorus co-doped bamboo charcoal, 25-40 parts of zinc-modified phenolic resin, and 5-10 parts of asphalt. The nitrogen-phosphorus co-doped bamboo charcoal contains 1.5-3.5% nitrogen by mass, 0.5-2.0% phosphorus by mass, and zinc in the form of ZnO or Zn-N. x -C coordination structures are present, with a mass fraction of 0.1-1.0%.

[0006] The interlayer spacing of the negative electrode material of this invention is 0.38-0.42 nm, and the specific surface area is 3-15 m². 2 g. The negative electrode material has a multi-level pore structure consisting of micropores, mesopores and macropores, of which closed pores account for 40-60% of the total pore volume; the micropore diameter is <2nm, the mesopore diameter is 2-50nm, and the macropore diameter is >50nm.

[0007] The preparation method of the above-mentioned biomass-based carbon anode material includes the following steps: S1. After pretreating bamboo charcoal, a nitrogen-phosphorus co-doped bamboo charcoal precursor is prepared by hydrothermal reaction with a nitrogen source and a phosphorus source. S2. Under alkaline catalytic conditions, phenol, formaldehyde and zinc source are polymerized to synthesize zinc-modified phenolic resin. S3. A composite slurry was prepared by mixing nitrogen and phosphorus co-doped bamboo charcoal precursor, asphalt and zinc modified phenolic resin, and then formed a three-dimensional network structure precursor by segmental cross-linking and curing. S4. The three-dimensional network structure precursor is subjected to programmed pyrolysis under an inert atmosphere to obtain pyrolysis products. The programmed pyrolysis includes a low-temperature decomposition stage, a medium-temperature activation and doping stabilization stage, and a high-temperature graphitization and structural reconstruction stage. S5. The pyrolysis products are acid-washed to obtain the negative electrode material.

[0008] Preferably, the bamboo charcoal pretreatment in S1 is as follows: the bamboo charcoal is pulverized to 100-200 mesh, and then treated with a 5-10 wt% nitric acid solution at 80-100 ppm. Reflux treatment for 2-4 hours, wash until neutral, then rinse at 100-120 °C. Dry for 8-12 hours.

[0009] Preferably, the nitrogen source in S1 includes one of urea, melamine, and dicyandiamide, and the phosphorus source includes one of phytic acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0010] Preferably, the mass ratio of bamboo charcoal, nitrogen source, and phosphorus source in S1 is 1:(0.5-1.5):(0.2-0.8); the hydrothermal reaction conditions are 160-200 °C. The reaction is carried out for 4-8 hours.

[0011] Preferably, the molar ratio of formaldehyde to phenol in S2 is 1.2-1.6:1, and the amount of zinc source added is 5%-15% of the mass of phenol. The zinc source includes one of zinc acetate, zinc nitrate, and zinc chloride.

[0012] Preferably, the catalyst used for alkaline catalysis in S2 is sodium hydroxide, and the amount added is 2-5% of the mass of phenol.

[0013] Preferably, the polymerization reaction in S2 is as follows: formaldehyde and phenol are first reacted at 70-90°C. The reaction is carried out for 1-3 hours, and then a zinc source is added to continue the reaction for 0.5-1.5 hours.

[0014] Preferably, the segmented crosslinking and curing in S3 includes: a first stage of low-temperature curing, at 80-100°C. Insulate at room temperature for 4-6 hours; second stage: hot pressing and curing at 150-180°C. Keep warm for 2-4 hours under 5-10 MPa pressure.

[0015] Preferably, when preparing the composite slurry in S3, the dispersion speed is 3000-5000 rpm and the dispersion time is 30-60 min.

[0016] Preferably, the parameters for each stage of programmed pyrolysis in S4 are as follows: Low-temperature decomposition stage: 1-2 Heat at a rate of 500-600°C per minute. Keep warm for 1-2 hours; Intermediate temperature activation and doping stabilization stage: 3-5 Heat at a rate of 800-1000 min Keep warm for 1 hour; High-temperature graphitization and structural reconstruction stage: 2-3 Heat at a rate of 1300-1500 min Keep warm for 2-3 hours.

[0017] Preferably, the pickling treatment in S5 is as follows: using 1-2M hydrochloric acid solution at 60-80°C. Soak for 2-4 hours, wash until neutral, then rinse at 100-120°C. Dry for 6-10 hours.

[0018] The beneficial effects of this invention are: (1) This invention achieves synergistic enhancement of bamboo charcoal through nitrogen and phosphorus co-doping. The introduction of nitrogen atoms forms active sites such as pyridine N, pyrrole N and graphite N, while n-type doping improves electronic conductivity. The atomic radius of phosphorus atoms is larger than that of carbon, and after doping, the carbon interlayer spacing is significantly expanded, reducing the sodium ion migration barrier. Furthermore, the formation of NP bonds regulates the local electronic structure of carbon materials, further enhancing the sodium ion adsorption capacity. The two work together to improve the reversible capacity of the anode material.

[0019] (2) This invention achieves multiple functional integration through zinc-modified phenolic resin. Zinc plays a triple role in the pyrolysis process: first, the nano-ZnO formed at low temperature acts as a pore-forming template, leaving abundant mesopores after volatilization at high temperature, thus optimizing ion transport channels; second, it acts as a graphitization catalyst, promoting the formation of a locally ordered conductive network of the carbon skeleton and improving the electronic conductivity of the negative electrode material; third, the formed Zn-N x -C coordination structure serves as an additional active site, enhancing sodium ion adsorption and storage; the three work synergistically to improve rate performance and cycle stability.

[0020] (3) The programmed pyrolysis of this invention achieves multi-objective synergistic control. The low-temperature decomposition stage ensures the full decomposition and cross-linking of the precursor. The medium-temperature activation and doping stabilization stage completes the stable solid solution of the dopant elements. The high-temperature graphitization and structural reconstruction stage precisely controls the interlayer spacing and the content of closed pores, of which 1300-1500 The high-temperature range allows for the optimal allocation of ramp capacity and platform capacity, resolving the contradiction between high capacity and high initial efficiency.

[0021] (4) This invention uses bamboo charcoal as a biomass raw material, which is widely available and inexpensive. Combined with the composite bonding effect of zinc-modified phenolic resin and asphalt, it improves the material's formability and structural stability. The preparation process does not require special equipment, the programmed pyrolysis parameters are easy to scale up industrially, and the post-processing steps are simple, thus having both environmental and economic benefits.

[0022] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0024] This invention provides a biomass-based carbon anode material. The anode material comprises, by weight, 50-70 parts of nitrogen-phosphorus co-doped bamboo charcoal, 25-40 parts of zinc-modified phenolic resin, and 5-10 parts of asphalt. The nitrogen-phosphorus co-doped bamboo charcoal contains 1.5-3.5% nitrogen by mass, 0.5-2.0% phosphorus by mass, and zinc in the form of ZnO or Zn-N. x -C coordination structures are present, with a mass fraction of 0.1-1.0%.

[0025] The interlayer spacing of the negative electrode material of this invention is 0.38-0.42 nm, and the specific surface area is 3-15 m². 2 g. The negative electrode material has a multi-level pore structure consisting of micropores, mesopores and macropores, of which closed pores account for 40-60% of the total pore volume; the micropore diameter is <2nm, the mesopore diameter is 2-50nm, and the macropore diameter is >50nm.

[0026] The preparation method of the above-mentioned biomass-based carbon anode material includes the following steps: S1. After pretreating bamboo charcoal, a nitrogen-phosphorus co-doped bamboo charcoal precursor is prepared by hydrothermal reaction with a nitrogen source and a phosphorus source. S2. Under alkaline catalytic conditions, phenol, formaldehyde and zinc source are polymerized to synthesize zinc-modified phenolic resin. S3. A composite slurry was prepared by mixing nitrogen and phosphorus co-doped bamboo charcoal precursor, asphalt and zinc modified phenolic resin, and then formed a three-dimensional network structure precursor by segmental cross-linking and curing. S4. The three-dimensional network structure precursor is subjected to programmed pyrolysis under an inert atmosphere to obtain pyrolysis products. The programmed pyrolysis includes a low-temperature decomposition stage, a medium-temperature activation and doping stabilization stage, and a high-temperature graphitization and structural reconstruction stage. S5. The pyrolysis products are acid-washed to obtain the negative electrode material.

[0027] Preferably, the bamboo charcoal pretreatment in S1 is as follows: the bamboo charcoal is pulverized to 100-200 mesh, and then treated with a 5-10 wt% nitric acid solution at 80-100 ppm. Reflux treatment for 2-4 hours, wash until neutral, then rinse at 100-120 °C. Dry for 8-12 hours.

[0028] Preferably, the nitrogen source in S1 includes one of urea, melamine, and dicyandiamide, and the phosphorus source includes one of phytic acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0029] In this invention, nitrogen atoms have a stronger electron attraction ability than carbon atoms. After being doped into the carbon framework, nitrogen atoms exist mainly in three stable chemical states: pyridine N, pyrrole N, and graphite N. Pyridine N is located at the edge of the carbon material and forms a strong adsorption effect with sodium ions through lone pair electrons, significantly increasing the number of active sites. Pyrrole N exists in the five-membered ring structure, and the unpaired electrons of its adjacent carbon atoms can form coordinate bonds with sodium ions, further enhancing the adsorption ability. Moreover, this site has good structural stability. Graphite N replaces carbon atoms in the carbon framework and injects free electrons into the carbon material through n-type doping, causing the Fermi level to shift to the vicinity of the conduction band and improving electronic conductivity.

[0030] Phosphorus atoms have a significantly larger radius than carbon atoms. When doped, they disrupt the ordered arrangement of the carbon skeleton, increase the interlayer spacing, and lower the sodium ion insertion barrier. Simultaneously, phosphorus atoms form NP covalent bonds with nitrogen atoms. These bonds can regulate the local electron cloud density of carbon materials, optimize sodium ion adsorption energy, and enhance charge storage capacity. Furthermore, the introduction of phosphorus atoms can suppress nitrogen loss during high-temperature pyrolysis, improving nitrogen retention.

[0031] Preferably, the mass ratio of bamboo charcoal, nitrogen source, and phosphorus source in S1 is 1:(0.5-1.5):(0.2-0.8); the hydrothermal reaction conditions are 160-200 °C. The reaction is carried out for 4-8 hours.

[0032] Preferably, the molar ratio of formaldehyde to phenol in S2 is 1.2-1.6:1, and the amount of zinc source added is 5%-15% of the mass of phenol. The zinc source includes one of zinc acetate, zinc nitrate, and zinc chloride.

[0033] In this invention, during the low-temperature stage of programmed pyrolysis, the zinc source first decomposes into Zn(OH)2, and then further decomposes to generate nano-ZnO particles. These particles are uniformly dispersed in the carbon precursor, forming a ZnO-carbon composite structure. Upon entering the high-temperature stage, ZnO is reduced by carbon to zinc vapor and volatilizes from the carbon framework, leaving mesoporous channels with a diameter of 10-50 nm inside the carbon material. This in-situ pore-forming mechanism can precisely control the number and distribution of mesopores, ensuring that the mesopore volume accounts for 30-40% of the total pore volume, significantly shortening the sodium ion transport path, improving the ion diffusion coefficient, and solving the bottleneck problem of slow ion transport in traditional hard carbon. In the intermediate-temperature stage, some undecomposed ZnO undergoes a coordination reaction with nitrogen-doped carbon to form Zn-N... x The -C coordination structure exhibits catalyst-like properties: firstly, it acts as a charge transfer medium, reducing the charge transfer resistance during the sodium ion insertion / extraction process; secondly, it serves as an additional active site, enhancing the adsorption capacity of sodium ions; and it also catalyzes the local graphitization of the carbon skeleton, forming a small amount of graphite microcrystals in the disordered carbon structure, further improving electronic conductivity.

[0034] Preferably, the catalyst used for alkaline catalysis in S2 is sodium hydroxide, and the amount added is 2-5% of the mass of phenol.

[0035] Preferably, the polymerization reaction in S2 is as follows: formaldehyde and phenol are first reacted at 70-90°C. The reaction is carried out for 1-3 hours, and then a zinc source is added to continue the reaction for 0.5-1.5 hours.

[0036] Preferably, the segmented crosslinking and curing in S3 includes: a first stage of low-temperature curing, at 80-100°C. Insulate at room temperature for 4-6 hours; second stage: hot pressing and curing at 150-180°C. Keep warm for 2-4 hours under 5-10 MPa pressure.

[0037] Preferably, when preparing the composite slurry in S3, the dispersion speed is 3000-5000 rpm and the dispersion time is 30-60 min.

[0038] Preferably, the parameters for each stage of programmed pyrolysis in S4 are as follows: Low-temperature decomposition stage: 1-2 Heat at a rate of 500-600°C per minute. Keep warm for 1-2 hours; this allows the resin and asphalt to fully decompose and cross-link, and zinc species to form nano-ZnO in situ.

[0039] Intermediate temperature activation and doping stabilization stage: 3-5 Heat at a rate of 800-1000 min Incubate at this temperature for 1 hour; nitrogen and phosphorus functional groups are stably doped into the carbon framework, and ZnO is partially reduced to form Zn-N. x -C coordination structure.

[0040] High-temperature graphitization and structural reconstruction stage: 2-3 Heat at a rate of 1300-1500 min Insulate for 2-3 hours. Adjust the interlayer spacing and the content of sealed pores to allow residual zinc species to volatilize and escape, creating pores in situ.

[0041] In the programmed pyrolysis process, this invention forms a multi-level pore structure of micropores-mesopores-macropores through the synergistic effect of ZnO template pore-forming (mesopores), precursor decomposition (micropores), and carbon skeleton shrinkage (macropores), thereby increasing the specific surface area of ​​the anode material and increasing the number of active sites.

[0042] Preferably, the pickling treatment in S5 is as follows: using 1-2M hydrochloric acid solution at 60-80°C. Soak for 2-4 hours, wash until neutral, then rinse at 100-120°C. Dry for 6-10 hours.

[0043] Example 1 This invention provides a biomass-based carbon anode material, prepared by the following method, comprising: S1. Crush the bamboo charcoal to 100 mesh, and then heat it with a 5wt% nitric acid solution at 80°C. Reflux treatment for 2 hours, wash until neutral, then at 100 Dry for 8 hours; disperse the pretreated bamboo charcoal, urea, and phytic acid in deionized water at a mass ratio of 1:0.5:0.2 to prepare a mixed solution; transfer the mixed solution to a hydrothermal reactor and heat at 160°C. The reaction was carried out for 4 hours, cooled, filtered, washed, and then carried out at 100 °C. After drying for 6 hours, nitrogen and phosphorus co-doped bamboo charcoal was obtained.

[0044] S2. Add phenol and deionized water to a three-necked flask and heat to 60°C. Add sodium hydroxide at 2% of phenol's mass as a catalyst and stir until completely dissolved; slowly add formaldehyde solution (formaldehyde to phenol molar ratio of 1.2:1), and after the addition is complete, raise the temperature to 70°C. The reaction was carried out for 1 hour; then 5% zinc acetate (by mass of phenol) was added, and the reaction was continued for 0.5 hours. The mixture was then cooled to room temperature to obtain zinc-modified phenolic resin.

[0045] S3. Mix 50 parts of nitrogen-phosphorus co-doped bamboo charcoal, 5 parts of asphalt, and 25 parts of zinc-modified phenolic resin, add an appropriate amount of deionized water, and disperse in a high-speed disperser at 3000 rpm for 30 minutes to form a uniform composite slurry. Then... Segmented cross-linking and curing, first stage low-temperature curing: The composite slurry is placed in an oven and cured at 80°C. The material is kept at a low temperature for 4 hours to remove moisture and achieve initial cross-linking. The second stage involves hot-pressing curing: the pre-cured material is transferred to a hot press and heated at 150°C. The precursor was kept at 5 MPa pressure for 2 hours to form a dense three-dimensional network structure.

[0046] S4. The three-dimensional network structure precursor is placed in a tube furnace and subjected to programmed pyrolysis (i.e., temperature-increasing carbonization) under an argon atmosphere. The specific process is as follows: Low-temperature decomposition stage: with 1 Heat up to 500 at a rate of min Keep warm for 1 hour; Intermediate-temperature activation and doping stabilization stage: with 3 Heat up to 800 at a minimum rate. Keep warm for 1 hour; High-temperature graphitization and structural reconstruction stage: with 2 Heat up to 1300 at a rate of min The mixture was kept at this temperature for 2 hours to obtain the pyrolysis products.

[0047] S5. Dissolve the pyrolysis products in 1M hydrochloric acid solution at 60°C. Soak for 2 hours, wash until neutral, and then rinse at 100°C. After drying for 6 hours, the negative electrode material was obtained.

[0048] Example 2 This invention provides a biomass-based carbon anode material, prepared by the following method, comprising: S1. Crush the bamboo charcoal to 150 mesh, and then heat it with an 8 wt% nitric acid solution at 90°C. After reflux treatment for 3 hours and washing until neutral, rinse at 110°C. The bamboo charcoal was dried for 10 hours. The pretreated bamboo charcoal, melamine, and ammonium dihydrogen phosphate were dispersed in deionized water at a mass ratio of 1:1.0:0.5 to prepare a mixed solution. The mixed solution was transferred to a hydrothermal reactor and heated at 180°C. The reaction was carried out for 6 hours, cooled, filtered, washed, and then discharged at 110 °C. After drying for 8 hours, nitrogen and phosphorus co-doped bamboo charcoal was obtained.

[0049] S2. Add phenol and deionized water to a three-necked flask and heat to 50°C. Add sodium hydroxide at 4% of the phenol mass as a catalyst and stir until completely dissolved; slowly add formaldehyde solution (molar ratio of formaldehyde to phenol is 1.4:1), and after the addition is complete, raise the temperature to 80°C. The reaction was carried out for 2 hours; zinc nitrate (10% by weight of phenol) was added, and the reaction was continued for 1 hour. The mixture was then cooled to room temperature to obtain zinc-modified phenolic resin.

[0050] S3. Mix 60 parts of nitrogen-phosphorus co-doped bamboo charcoal, 8 parts of asphalt, and 32 parts of zinc-modified phenolic resin, add an appropriate amount of deionized water, and disperse in a high-speed disperser at 4000 rpm for 45 minutes to form a uniform composite slurry. Then, perform segmented cross-linking and curing. The first stage is low-temperature curing: place the composite slurry in an oven and heat at 90°C. The material is kept at a low temperature for 5 hours to remove moisture and achieve initial cross-linking. The second stage involves hot pressing and curing: the pre-cured material is transferred to a hot press and heated at 165°C. The precursor was kept at 8MPa pressure for 3 hours to form a dense three-dimensional network structure.

[0051] S4. The three-dimensional network structure precursor is placed in a tube furnace and subjected to programmed pyrolysis (i.e., temperature-increasing carbonization) under a nitrogen atmosphere. The specific process is as follows: Low-temperature decomposition stage: at 1.5 Heat to 550 at a minimum rate. Keep warm for 1.5 hours; Intermediate-temperature activation and doping stabilization stage: with 4 Heat up to 900 at a rate of min Keep warm for 1 hour; High-temperature graphitization and structural reconstruction stage: with 2 Heat up to 1400 at a rate of min The mixture was kept at this temperature for 2.5 hours to obtain the pyrolysis products.

[0052] S5. The pyrolysis products were treated with 2M hydrochloric acid solution at 70°C. Soak for 3 hours, wash until neutral, and then rinse at 110°C. After drying for 8 hours, the negative electrode material was obtained.

[0053] Example 3 This invention provides a biomass-based carbon anode material, prepared by the following method, comprising: S1. Crush the bamboo charcoal to 200 mesh, and then precipitate it with a 10wt% nitric acid solution at 100°C. After reflux treatment for 4 hours and washing until neutral, it is then rinsed at 120°C. The bamboo charcoal was dried for 12 hours. The pretreated bamboo charcoal, dicyandiamide, and diammonium hydrogen phosphate were dispersed in deionized water at a mass ratio of 1:1.5:0.8 to prepare a mixed solution. The mixed solution was transferred to a hydrothermal reactor and heated at 200°C. The reaction was carried out for 8 hours, cooled, filtered, washed, and then carried out at 120°C. After drying for 10 hours, nitrogen and phosphorus co-doped bamboo charcoal was obtained.

[0054] S2. Add phenol and deionized water to a three-necked flask and heat to 60°C. Add sodium hydroxide solution (5% by mass of phenol) as a catalyst and stir until completely dissolved. Slowly add formaldehyde solution (molar ratio of formaldehyde to phenol: 1.6:1). After the addition is complete, heat to 90°C. The reaction was carried out for 3 hours. Zinc chloride at 15% of the phenol mass was added, and the reaction was continued for 1.5 hours. After cooling to room temperature, zinc-modified phenolic resin was obtained.

[0055] S3. Mix 70 parts of nitrogen-phosphorus co-doped bamboo charcoal, 10 parts of asphalt, and 40 parts of zinc-modified phenolic resin, add an appropriate amount of deionized water, and disperse in a high-speed disperser at 5000 rpm for 60 minutes to form a uniform composite slurry. Then, perform segmented cross-linking and curing. The first stage is low-temperature curing: place the composite slurry in an oven and heat at 100°C. The material is kept at a low temperature for 6 hours to remove moisture and achieve initial cross-linking. The second stage involves hot pressing and curing: the pre-cured material is transferred to a hot press and pressed at 180°C. The precursor was kept at 10 MPa pressure for 4 hours to form a dense three-dimensional network structure.

[0056] S4. The three-dimensional network structure precursor is placed in a tube furnace and subjected to programmed pyrolysis (i.e., temperature-increasing carbonization) under an argon atmosphere. The specific process is as follows: Low-temperature decomposition stage: with 2 Heat up to 600 at a constant rate. Keep warm for 2 hours; Intermediate-temperature activation and doping stabilization stage: with 5 Heat up to 1000 min rate Keep warm for 1 hour; High-temperature graphitization and structural reconstruction stage: with 3 Heat up to 1500 at a rate of min The mixture was kept at this temperature for 3 hours to obtain the pyrolysis products.

[0057] S5. The pyrolysis products were treated with 2M hydrochloric acid solution at 80°C. Soak for 4 hours, wash until neutral, and then rinse at 120°C. After drying for 10 hours, the negative electrode material was obtained.

[0058] Comparative Example 1 Based on Example 2, the difference is that in step S1, the bamboo charcoal was not pretreated with nitric acid and subjected to a nitrogen-phosphorus co-doping hydrothermal reaction, and the original bamboo charcoal powder was used directly. All other aspects are the same as in Example 2.

[0059] Comparative Example 2 Based on Example 2, the difference is that zinc nitrate was not added in the phenolic resin synthesis process in step S2, and the rest is the same as in Example 2.

[0060] Comparative Example 3 Based on Example 2, the difference lies in that the final temperature of the high-temperature graphitization and structural reconstruction stage in step S4 is 1200°C. The heat preservation time is 2.5 hours.

[0061] Performance testing The negative electrode materials, conductive agents and binders prepared in Examples 1-3 and Comparative Examples 1-3 were mixed in a mass ratio of 80-90:5-10:5-10, and an appropriate amount of deionized water or N-methylpyrrolidone was added. The mixture was stirred to form a uniform slurry, which was then coated onto copper foil. After drying and rolling, the slurry was made into a sodium-ion battery negative electrode sheet.

[0062] A CR2032 coin cell system was used, with the negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 as the working electrode, and a sodium metal sheet as the counter electrode and reference electrode. WhatmanGF D. Glass fiber is used as the diaphragm, 1 mol Using NaPF6 / EC:DMC:DEC (volume ratio 1:1:1) as the electrolyte, the battery was assembled in an argon glove box (water and oxygen content <0.1ppm). A Blue Electric CT2001A battery testing system was used, operating at 0.1A within the voltage range of 0.01-3.0V. Constant current charge-discharge tests are performed using g current density. Reversible capacity is measured by the actual capacity during the discharge process. Initial coulombic efficiency = (initial discharge capacity / initial charge capacity) 100%. The results are shown in Table 1.

[0063] Table 1. Reversible capacity and first coulombic efficiency of different anode materials As shown in Table 1, the reversible capacity of Examples 1-3 all exceeds 390mAh. g, initial Coulomb efficiency The reversible capacity was 89%, with Example 2 being the best, and all were superior to Comparative Examples 1-3. The reversible capacity and initial coulombic efficiency of Comparative Examples 1 and 2 both decreased, indicating that the synergistic effect of nitrogen-phosphorus co-doping, zinc modification, and programmed pyrolysis can effectively improve charge storage capacity and interface stability. The reversible capacity of Comparative Example 3 was close to that of the examples, but the initial coulombic efficiency was only 80%, because the low-temperature pyrolysis resulted in insufficient closed-pore ratio, aggravated electrolyte side reactions, and increased irreversible capacity.

[0064] Based on the aforementioned button cell battery, the Landon CT2001A battery testing system was used to test the battery at 0.1A increments within the 0.01-3.0V voltage range. g, 0.5A g、1A g、2A g、5A The circuit is subjected to charge-discharge cycles at a current density of g (5 cycles per current density), and finally restored to 0.1A. The discharge capacity was recorded after 5 cycles at a current density of g, and the capacity retention rate was calculated. The results are shown in Table 2.

[0065] Table 2 Rate capacity (mAh) of different anode materials at various current densities g) As shown in Table 2, Example 2 exhibits the best performance across the entire current density range, at 5A. Even at high magnification, it still has 258mAh capacity. The capacity recovered to 0.1 A / g, with a capacity decay of only 1.2%, demonstrating its excellent ion transport efficiency and structural stability. This is because the hierarchical porous structure formed by zinc modification provides fast ion channels, and the enhanced electronic conductivity from nitrogen and phosphorus co-doping reduces transport resistance. Comparative Examples 1 and 2 showed significant capacity decay at high rates, with a capacity of 5 A / g. The capacity at g times is all below 210mAh. g. Due to the lack of NP co-doping, the electronic conductivity is low, and charge transfer is hindered; without Zn modification, the mesopore volume is insufficient, ion diffusion is slow, and capacity decay is significant at high rates. Comparative Example 3's high-rate performance is weaker than Example 2's because the excessive interlayer spacing affects structural stability.

[0066] Based on the aforementioned button cell battery, the Blue Electric CT2001A battery testing system was used to test the battery at 1A within the voltage range of 0.01-3.0V. A constant current density is applied for 1000 charge-discharge cycles. The discharge capacity of each cycle is recorded, and the capacity retention rate is calculated for different cycle numbers (capacity retention rate = (discharge capacity at the nth cycle)). (Second discharge capacity) 100%, taking the second capacity as the baseline to exclude the influence of the first activation).

[0067] Table 3 Different negative electrode materials at 1A Cyclic performance at current density g As shown in Table 3, Example 2 exhibits the best cyclic stability, with a capacity retention of 78% after 1000 cycles, significantly higher than the other comparative examples. This is because Zn-N x -C coordination structures provide stable active sites, reducing active material shedding during cycling; the proportion of closed pores inhibits electrolyte erosion and reduces the rate of structural degradation. Comparative Examples 1 and 2 exhibited faster cycle decay, with retention rates of only 65% ​​and 70% after 1000 cycles, respectively, due to their lack of stable active sites and structural support. Comparative Example 3 showed a significant capacity decrease in the later stages of cycling, which was attributed to insufficient closed pore ratio leading to accelerated electrolyte erosion.

[0068] Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) tests were performed on the above-mentioned coin cells using a Chenhua CHI660E electrochemical workstation. The EIS test frequency range was 10... 6 -10 -2 A Hz AC signal with an amplitude of 5mV is applied, and an equivalent circuit is fitted using ZView software (R... s (R ctCPE)W) Extraction charge transfer resistor (R) CT); CV test scan rate 0.1-1.0mV For a voltage range of 0.01-3.0V, the ion diffusion coefficient was calculated using the Randles-Sevcik equation. The negative electrode material was pressed into a circular sheet with a diameter of 10mm and a thickness of 1-2mm (pressure 10MPa, holding for 5min). An RTS-8 four-probe tester was used, with a current of 100mA applied, and the voltage value was recorded. The result was calculated using the formula (σ=L...). (RS), where L is the thickness of the negative electrode material, R is the test resistance, and S is the cross-sectional area of ​​the negative electrode material, is used to calculate the electronic conductivity. The results are shown in Table 4.

[0069] Table 4 Charge transfer resistance, ion diffusion coefficient and electronic conductivity of different negative electrode materials As shown in Table 4, the charge transfer resistance of Example 2 is only 152. The ion diffusion coefficient reaches 3.5. 10 -10 cm 2 The resistivity of the sample is 4.1 times that of Comparative Example 1. Nitrogen-phosphorus co-doping enhances electronic conductivity and reduces resistance through n-type doping, while zinc modification creates mesopores that shorten ion transport paths and increase the diffusion coefficient. These two factors work synergistically to address the bottleneck of slow ion transport in traditional hard carbon. Comparative Example 1 has a resistivity as high as 480 Ω. Due to the lack of doping modification, it has low electronic conductivity and cannot transfer charge rapidly; comparative example 2 has an ion diffusion coefficient of only 1.3. 10 -10 cm 2 s, due to the lack of mesoporous channels, ions need to migrate over long distances; comparative example 3 has a slightly higher resistance because the graphitization degree is low due to low-temperature pyrolysis, and the electronic conduction network is incomplete.

[0070] The McMurray Ticco ASAP 2460 physical adsorption instrument was used, with a negative electrode material of 300... Vacuum degassing for 4 hours, -196 Nitrogen adsorption-desorption experiments were conducted, and the specific surface area was calculated using the BET (Brunauer-Emmett-Teller) model. In conjunction with an AutoPore IV 9500 mercury porosimeter, the mesopore volume (2-50 nm) was calculated using the BJH model in the nitrogen adsorption method, and the micropore volume (<2 nm) was calculated using the t-plot method; the macropore volume (>50 nm) was calculated using the mercury porosimeter method (pressure 0-414 MPa); the closed pore ratio was calculated as (total pore volume - open pore volume). Total capacity 100% (total pore volume was calculated using true density and apparent density, with true density tested using the AccuPycII1340 helium displacement method), results are shown in Table 5.

[0071] Table 5 Microstructure properties of different anode materials As shown in Table 5, the specific surface area of ​​Examples 1-3 is 8.5-11.8 m². 2 g, which avoids both excessively small specific surface area and insufficient active sites, and excessively large specific surface area and accelerated electrolyte decomposition, as in Example 2, 10.2m 2 Achieving a balance between active site and interface stability is crucial for its high capacity and high first-time efficiency. Comparative Examples 1 and 2 have specific surface areas < 7 m². 2 g, fewer active sites, lower capacity than in the example; Scale 3 has a specific surface area of ​​14.8 m². 2 Although g has many active sites, its large interfacial reaction area results in a first coulombic efficiency of only 80%.

[0072] In Example 2, the distribution of micropores, mesopores, and macropores is balanced, with closed pores accounting for 52%. Micropores provide active sites, mesopores accelerate ion transport and increase the rate of change, macropores alleviate volume expansion and enhance circulation, and closed pores suppress electrolyte side reactions and improve initial efficiency, forming a synergistic system of storage-transport-stability. Comparative Examples 1 and 2 have mesopore volumes <0.022 cm³. 3 g. Insufficient ion channels result in poor rate and cycle performance; in Comparative Example 3, the proportion of closed pores is only 35%, and the large number of open pores leads to electrolyte erosion and low initial efficiency.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A biomass-based carbon anode material, characterized in that: The negative electrode material, by weight, comprises 50-70 parts of nitrogen-phosphorus co-doped bamboo charcoal, 25-40 parts of zinc-modified phenolic resin, and 5-10 parts of pitch. The nitrogen-phosphorus co-doped bamboo charcoal contains 1.5-3.5% nitrogen by mass, 0.5-2.0% phosphorus by mass, and zinc is expressed as ZnO or Zn-N. x -C coordination structures are present, with a mass fraction of 0.1-1.0%.

2. A method for preparing the biomass-based carbon anode material as described in claim 1, characterized in that: Includes the following steps: S1. After pretreating bamboo charcoal, a nitrogen-phosphorus co-doped bamboo charcoal precursor is prepared by hydrothermal reaction with a nitrogen source and a phosphorus source. S2. Under alkaline catalytic conditions, phenol, formaldehyde and zinc source are polymerized to synthesize zinc-modified phenolic resin. S3. A composite slurry was prepared by mixing nitrogen and phosphorus co-doped bamboo charcoal precursor, asphalt and zinc modified phenolic resin, and then formed a three-dimensional network structure precursor by segmental cross-linking and curing. S4. The three-dimensional network structure precursor is subjected to programmed pyrolysis under an inert atmosphere to obtain pyrolysis products. The programmed pyrolysis includes a low-temperature decomposition stage, a medium-temperature activation and doping stabilization stage, and a high-temperature graphitization and structural reconstruction stage. S5. The pyrolysis products are acid-washed to obtain the negative electrode material.

3. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: The bamboo charcoal pretreatment in S1 is as follows: pulverize the bamboo charcoal to 100-200 mesh, then soak it in a 5-10 wt% nitric acid solution at 80-100 ppm. Reflux treatment for 2-4 hours, wash until neutral, then rinse at 100-120 °C. Dry for 8-12 hours.

4. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: The nitrogen source in S1 includes one of urea, melamine, and dicyandiamide, and the phosphorus source includes one of phytic acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

5. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: In S1, the mass ratio of bamboo charcoal, nitrogen source, and phosphorus source is 1:(0.5-1.5):(0.2-0.8); the hydrothermal reaction conditions are 160-200 °C. The reaction is carried out for 4-8 hours.

6. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: The molar ratio of formaldehyde to phenol in S2 is 1.2-1.6:1, and the amount of zinc source added is 5%-15% of the mass of phenol. The zinc source includes one of zinc acetate, zinc nitrate, and zinc chloride.

7. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: The polymerization reaction in S2 is as follows: first, formaldehyde and phenol are reacted at 70-90°C. The reaction is carried out for 1-3 hours, and then a zinc source is added to continue the reaction for 0.5-1.5 hours.

8. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: S3 segmented crosslinking and curing includes: the first stage of low-temperature curing, at 80-100°C. Insulate at room temperature for 4-6 hours; second stage: hot pressing and curing at 150-180°C. Keep warm for 2-4 hours under 5-10 MPa pressure.

9. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: The parameters for each stage of programmed pyrolysis in S4 are as follows: Low-temperature decomposition stage: 1-2 Heat at a rate of 500-600°C per minute. Keep warm for 1-2 hours; Mid-temperature activation and doping stabilization stage: 3-5 Heat at a rate of 800-1000 min Keep warm for 1 hour; High-temperature graphitization and structural reconstruction stage: 2-3 Heat at a rate of 1300-1500 min Keep warm for 2-3 hours.

10. The method for preparing a biomass-based carbon anode material according to claim 2, characterized in that: The pickling process in S5 involves using a 1-2M hydrochloric acid solution at 60-80°C. Soak for 2-4 hours, wash until neutral, then rinse at 100-120°C. Dry for 6-10 hours.

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