Preparation method of biomass-based hard carbon material and application of biomass-based hard carbon material in sodium ion battery

Abstract

The application discloses a preparation method of a biomass-based hard carbon material and application of the biomass-based hard carbon material in a sodium ion battery, and relates to the technical fields of hard carbon material preparation and sodium ion batteries. The method takes bamboo as raw material, and prepares the hard carbon material with excellent electrochemical performance through simple pretreatment, oxidation modification, carbonization and joule heat post-treatment processes, and has the advantages of simple process flow, low energy consumption and environmental friendliness. The method comprises the following steps: step 1, acid solution pretreatment; step 2, oxidation modification treatment; step 3, low-temperature carbonization; and step 4, joule heat post-treatment. The combined preparation method simplifies the process flow, reduces the energy consumption, realizes accurate regulation and control of the structure and performance of the hard carbon material, and provides a brand-new idea for development of low-cost and high-performance negative electrode materials of the sodium ion battery.

Description

Technical Field

[0001] This invention relates to the fields of hard carbon material preparation and sodium-ion battery technology, specifically to a method for preparing hard carbon material using bamboo as a biomass raw material, and also to the application of the hard carbon material as a negative electrode material for sodium-ion batteries. Background Technology

[0002] With the increasing severity of the global energy crisis and environmental problems, the development of renewable energy and energy storage technologies has received widespread attention. Sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, have shown great application potential in large-scale energy storage, becoming an important supplement to lithium-ion batteries.

[0003] As a core component of sodium-ion batteries, the performance of the anode material directly determines the battery's energy density, cycle stability, and rate performance. Hard carbon materials, characterized by large interlayer spacing, structural stability, and low preparation cost, are currently a research hotspot in sodium-ion battery anode materials. Biomass resources, due to their renewability, environmental friendliness, and low cost, have become ideal raw materials for preparing hard carbon materials. Moso bamboo, as a biomass resource abundant in my country, has a fast growth rate, well-developed fiber structure, and high carbon content, possessing the potential to be converted into high-performance hard carbon materials.

[0004] Chinese patent CN116462176A discloses an ultrafast method for preparing hard carbon anode materials for sodium-ion batteries. This method uses bamboo biomass as raw material and employs the Joule heating effect to achieve rapid carbonization, resulting in a short carbonization time while maintaining good electrochemical performance. However, this method does not adequately pretreat the biomass raw material, failing to effectively remove metallic impurities and inorganic components, thus affecting the purity and electrochemical performance of the final hard carbon material.

[0005] Chinese patent CN119551660A discloses a method for preparing a sodium-ion battery anode material that balances high capacity and high initial efficiency. This method uses biomass as a precursor for the hard carbon anode material. The precursor is purified by acid washing, then pre-oxidized, and finally subjected to high-temperature secondary carbonization to obtain the hard carbon material. Although this method employs acid washing and pre-oxidation, the high-temperature carbonization process uses a traditional long-duration heating method, with carbonization time reaching several hours, resulting in high energy consumption. Furthermore, it is difficult to precisely control the microstructure of the material, limiting further improvements in the sodium storage performance of the hard carbon material.

[0006] Therefore, traditional methods for preparing biomass-based hard carbon materials often suffer from problems such as complex processes, high energy consumption, and difficulty in controlling the microstructure of the materials. This results in the sodium storage capacity, cycle stability, and rate performance of hard carbon materials failing to meet the application requirements of high-performance sodium-ion batteries. Furthermore, insufficient pretreatment of raw materials in some preparation processes makes it difficult to effectively remove impurities from the biomass, thus affecting the electrochemical performance of the final hard carbon material. Therefore, developing a simple, energy-efficient, and high-performance biomass-based hard carbon material preparation method is of great significance for promoting the industrial application of sodium-ion batteries. Summary of the Invention

[0007] To address the above problems, this invention proposes a method for preparing biomass-based hard carbon materials and their application in sodium-ion batteries. This method uses bamboo as raw material and prepares hard carbon materials with excellent electrochemical performance through simple pretreatment, oxidation modification, carbonization, and Joule heating post-treatment processes. The process is simple, energy-efficient, and environmentally friendly.

[0008] The technical solution of the present invention is as follows: the hard carbon material is prepared by using bamboo powder as a carbon source, through acid washing pretreatment, oxidation modification, nitrogen atmosphere carbonization and Joule heating posttreatment, and the hard carbon material includes the following steps: Step 1, acidic solution pretreatment: Before carbonization, the biomass raw material is added to an acidic solution and stirred. After solid-liquid separation, it is washed with water until neutral and dried to obtain acid-washed modified biomass raw material. Step 2, Oxidative Modification Treatment: The acid-washed modified biomass raw material is added to an oxidant solution and stirred. After solid-liquid separation, it is washed with water until neutral and dried to obtain the oxidized modified biomass raw material. Step 3, Low-temperature carbonization: The oxidized biomass raw material is placed in an inert atmosphere for carbonization treatment, heated to 500-700℃ at a heating rate of 5℃ / min, and held at this temperature for 1-5 hours; after the holding period, it is naturally cooled to room temperature to obtain the primary carbonization product. Step 4, Joule heating post-treatment: Nitrogen gas is introduced into the Joule heating reaction device of the primary carbonization product for protection, and DC power is used to rapidly heat the product to 1500°C and maintain the temperature for 20 seconds; after the treatment is completed, the power supply is stopped and the product is allowed to cool naturally to room temperature to obtain biomass-based hard carbon material.

[0009] Furthermore, the biomass raw material mentioned in step 1 is bamboo powder.

[0010] Furthermore, in step 1, the acidic solution is a sulfuric acid solution with a concentration of 0.5-2M, the stirring temperature is room temperature, the stirring speed is 400 r / min, and the stirring time is 12 h; the solid-liquid separation method in step 1 is vacuum filtration or centrifugation, the centrifugation speed is 3000~5000 r / min, and the centrifugation time is 5~10 min; the drying temperature in step 1 is 60℃, and the drying time is 12 h.

[0011] Furthermore, the oxidant in step 2 is hydrogen peroxide with a concentration of 3-10%, the stirring speed is 400 r / min, and the stirring time is 6 h; after filtration, the washing liquid is washed until it is neutral, the drying temperature is 60℃, and the drying time is 12 h.

[0012] Furthermore, the inert atmosphere mentioned in step 3 is nitrogen with a purity of ≥99.9% and a flow rate of 50~100mL / min.

[0013] Furthermore, the power supply for the Joule heat treatment in step 4 is a DC power supply with a current density of 10~20A / cm², a treatment temperature of 1500℃, and a treatment time of 20s.

[0014] Regarding the application of the above-prepared biomass-based hard carbon material in the anode of sodium-ion batteries: By mass percentage, 80-95% of the biomass-based hard carbon material, 3-10% of the conductive agent and 2-10% of the binder are mixed, a solvent is added to adjust the solid content of the slurry, and the mixture is coated on the surface of the metal current collector. After drying, a sodium-ion battery negative electrode sheet is obtained.

[0015] Furthermore, the conductive agent is superconducting carbon black, the binder is sodium carboxymethyl cellulose, the metal current collector is copper foil, the coating thickness is 50-200 μm, the drying temperature is 60-120°C, and the drying time is 6-24 h.

[0016] This invention's combined preparation method simplifies the process, reduces energy consumption, and achieves precise control over the structure and performance of hard carbon materials. It provides a novel approach for developing low-cost, high-performance anode materials for sodium-ion batteries. Compared to existing technologies, the advantages of this invention are: I. Through a step-by-step processing technology of "acid washing to remove impurities - oxidation modification - low-temperature carbonization - rapid Joule heating post-treatment", precise structural control of biomass raw materials into high-performance sodium storage hard carbon materials is achieved. The acid washing pretreatment effectively removes metal impurities and inorganic components, and the oxidation modification regulates the surface functional groups and pore structure, laying the foundation for the formation of excellent sodium storage structure.

[0017] Second, by combining low-temperature carbonization at 600℃ with Joule heating post-treatment at 1500℃, the biomass raw materials are fully carbonized, and the rapid high-temperature Joule heating optimizes the crystal structure and pore distribution of the hard carbon material, thereby improving the material's conductivity and sodium ion diffusion rate.

[0018] Third, the Joule heating rapid high-temperature post-treatment time is only 20 seconds, which is 99% shorter than the traditional long-time high-temperature carbonization process (2 hours), and the energy consumption is reduced by about 98%, which greatly reduces the production cost. In addition, the rapid high-temperature treatment optimizes the crystal structure and pore distribution of hard carbon materials, and improves the conductivity and sodium ion diffusion rate.

[0019] Fourth, the entire preparation process is simple, easy to operate, and environmentally friendly. The raw materials are widely available and inexpensive, making it easy to achieve large-scale production. This provides a new technical path for the cost reduction and high performance of sodium-ion battery anode materials. Attached Figure Description

[0020] Figure 1 is an X-ray diffraction (XRD) pattern of the biomass-based hard carbon material prepared in Example 1 of the present invention; Figure 2 is a charge-discharge curve of the hard carbon material prepared in Example 1 of the present invention as the negative electrode of a sodium-ion battery; Figure 3 shows the 100mA / g cycle stability test of the hard carbon material prepared in Example 1 of the present invention as a sodium-ion battery anode. Figure 4 shows the rate performance test results of the hard carbon material prepared in Example 1 of this invention as a negative electrode of a sodium-ion battery. Detailed Implementation

[0021] To clearly illustrate the technical features of the present invention, the present invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0022] All raw materials used in this invention are commercially available conventional products and have not undergone any special treatment.

[0023] Example 1, Step 1: Acid washing pretreatment of bamboo raw material: Weigh 20g of 30-mesh bamboo powder (commercially available, uniform particle size) and add it to 200mL of 1M sulfuric acid solution (prepared by diluting 98% concentrated sulfuric acid). Place the mixture on a magnetic stirrer and stir at 400r / min for 12h at room temperature. After stirring, perform solid-liquid separation by vacuum filtration, collect the solid product, and wash it repeatedly with ultrapure water until the pH of the washing solution is 7 (neutral). Then, place the solid product in an oven and dry it at 60℃ for 12h to obtain acid-modified bamboo powder. Step 2: Oxidation modification treatment of bamboo powder: Take 20g of the acid-washed modified bamboo powder obtained in step 1, add it to 200mL of 5% hydrogen peroxide solution (prepared by diluting commercially available 30% hydrogen peroxide), and stir at 400r / min for 6h. After the reaction is completed, collect the solid product by vacuum filtration, wash it with ultrapure water until the washing solution is neutral, and then dry it at 60℃ for 12h to obtain oxidized modified bamboo powder. Step 3, Carbonization treatment: The oxidized bamboo powder obtained in step 2 was placed in an inert atmosphere tube furnace, and nitrogen gas with a purity of 99.99% was introduced. The nitrogen gas flow rate was controlled at 80 mL / min, and the temperature was raised to 600℃ at a heating rate of 5℃ / min. The temperature was then maintained at this temperature for 3 hours. After the holding period, the heating device was turned off, and the nitrogen atmosphere was allowed to cool naturally to room temperature to obtain the primary carbonized product. Step 4, Joule heating post-treatment: The primary carbonization product obtained in step 3 was placed in a Joule heating reactor, protected by nitrogen gas, powered by a DC power supply, and the current density was controlled at 15 A / cm² to rapidly heat the product to 1500°C and maintain this temperature for 20 seconds. After the process was completed, the power supply was stopped and the product was allowed to cool naturally to room temperature to obtain biomass-based hard carbon material. Step 5: Preparation of electrode sheets: Weigh out 90% of hard carbon material, 5% of conductive agent SP (superconducting carbon black), and 5% of binder CMC (sodium carboxymethyl cellulose) by mass percentage, and mix them evenly in an agate mortar. Add an appropriate amount of deionized water, stir in a planetary ball mill for 3 hours, and adjust the solid content of the slurry to 20% to form a uniformly dispersed electrode slurry. Use a scraper to coat the electrode slurry onto the surface of a copper foil with a thickness of 12 μm, and then place the coated copper foil in an oven and dry it at 80°C for 12 hours. After drying, a sodium-ion battery negative electrode sheet is obtained. Step 6: Assembly and testing of sodium-ion batteries: In an argon-protected glove box (water and oxygen content ≤0.1ppm), a CR2032 coin cell sodium-ion battery was assembled using the negative electrode sheet prepared in step 5 as the working electrode (effective area 1.131cm²), a sodium metal sheet as the counter electrode and reference electrode, Celgard 2400 as the separator, and a 1M NaPF6 DIGLYME solution as the electrolyte. The battery's electrochemical performance was tested using a Newway battery testing system, with a test voltage range of 0-2.5V. The charge-discharge test current density was 20-2000mA / g, and the cycle stability test was conducted at a current density of 100 mA / g.

[0024] The XRD pattern of the biomass-based hard carbon material prepared in this embodiment is shown in the figure below. Figure 1As shown, the material exhibits typical hard carbon diffraction peaks, indicating its disordered layered structure; the electrochemical performance test results are as follows: Figure 2 The results show that the material has an initial charge capacity of 368.02 mAh / g at a current density of 20 mA / g and an initial coulombic efficiency of 90% (as shown in Table 1). It can still maintain a discharge capacity of 293.2 mAh / g at a high current density of 1000 mA / g, demonstrating excellent sodium storage performance.

[0025] Example 2 differs from Example 1 in that the Joule heat treatment temperature in step 4 is 1400°C, while the remaining steps are exactly the same as in Example 1, resulting in hard carbon material.

[0026] Electrochemical performance tests showed that the prepared hard carbon material had a reversible specific capacity of 332.87 mAh / g and a first-week coulombic efficiency of 86% (as shown in Table 1). The performance was better than that of the comparative example but slightly lower than that of Example 1, indicating that a Joule heat treatment temperature of 1500℃ is more conducive to obtaining high-performance hard carbon materials.

[0027] Example 3 differs from Example 1 in that the Joule heat treatment temperature in step 4 is 1600°C, while the remaining steps are exactly the same as in Example 1, resulting in hard carbon material.

[0028] Electrochemical performance tests showed that the reversible specific capacity of the prepared hard carbon material was 336.19 mAh / g, and the coulombic efficiency in the first week was 89% (as shown in Table 1). Due to the high temperature, the degree of graphitization of the material increased, the interlayer spacing decreased, and the sodium storage capacity decreased.

[0029] Comparative Example 1: Hard carbon material was prepared directly using bamboo powder without acid washing pretreatment or oxidation modification. Other conditions were the same as in Example 1, including the following steps: Weigh 20g of 2000-mesh bamboo powder and place it directly in a tube furnace under a nitrogen protective atmosphere. Heat it to 600℃ at a heating rate of 5℃ / min, hold it at that temperature for 3 hours, and then allow it to cool naturally to obtain the primary carbonization product. Then, perform a Joule heat treatment at 1500℃ for 20 seconds to obtain hard carbon material.

[0030] Since no acid washing and oxidation modification treatment was performed, the impurities in the bamboo raw material were not effectively removed and the surface structure was not optimized. According to the electrochemical performance test, the reversible specific capacity of the prepared hard carbon material was 323.05 mAh / g and the first-week coulombic efficiency was 86% (as shown in Table 1), which was significantly lower than that of Example 1.

[0031] Comparative Example 2 differs from Example 1 in that after carbonization in step 3, the material is carbonized by conventional heating at 1500 degrees Celsius for 2 hours to obtain hard carbon material. The remaining steps are exactly the same as in Example 1.

[0032] Since no Joule heat post-treatment was performed, the crystal structure and pore distribution of the material were not further optimized. Electrochemical performance tests showed that its reversible specific capacity was 309.27 mAh / g and the first-week coulombic efficiency was 92% (as shown in Table 1). Compared with Example 1, the sodium storage capacity was significantly reduced, indicating that Joule heat post-treatment can effectively optimize the structure and electrochemical performance of hard carbon materials.

[0033] The table below shows the charge-discharge data for preparing hard carbon anodes under different implementation cases.

[0034]

[0035] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A method for preparing a biomass-based hard carbon material, characterized in that, Includes the following steps: Step 1, acidic solution pretreatment: Before carbonization, the biomass raw material is added to an acidic solution and stirred. After solid-liquid separation, it is washed with water until neutral and dried to obtain acid-washed modified biomass raw material. Step 2, Oxidative Modification Treatment: The acid-washed modified biomass raw material is added to an oxidant solution and stirred. After solid-liquid separation, it is washed with water until neutral and dried to obtain the oxidized modified biomass raw material. Step 3, Low-temperature carbonization: The oxidized biomass raw material is placed in an inert atmosphere for carbonization treatment, heated to 500-700℃ at a heating rate of 5℃ / min, and held at this temperature for 1-5 hours; after the holding period, it is naturally cooled to room temperature to obtain the primary carbonization product. Step 4, Joule heating post-treatment: Nitrogen gas is introduced into the Joule heating reaction device of the primary carbonization product for protection, and DC power is used to rapidly heat the product to 1500°C and maintain the temperature for 20 seconds; after the treatment is completed, the power supply is stopped and the product is allowed to cool naturally to room temperature to obtain biomass-based hard carbon material.

2. The method for preparing a biomass-based hard carbon material according to claim 1, characterized in that, The biomass raw material mentioned in step 1 is bamboo powder.

3. The method for preparing a biomass-based hard carbon material according to claim 1, characterized in that, In step 1, the acidic solution is a sulfuric acid solution with a concentration of 0.5-2M. The stirring temperature is room temperature, the stirring speed is 400 r / min, and the stirring time is 12 h. The solid-liquid separation method in step 1 is vacuum filtration or centrifugation. The centrifugation speed is 3000~5000 r / min, and the centrifugation time is 5~10 min. The drying temperature in step 1 is 60℃, and the drying time is 12 h.

4. The method for preparing a biomass-based hard carbon material according to claim 1, characterized in that, The oxidant in step 2 is hydrogen peroxide with a concentration of 3-10%. The stirring speed is 400 r / min and the stirring time is 6 h. After filtration, the washing liquid is washed until it is neutral. The drying temperature is 60℃ and the drying time is 12 h.

5. The method for preparing a biomass-based hard carbon material according to claim 1, characterized in that, The inert atmosphere mentioned in step 3 is nitrogen with a purity of ≥99.9% and a flow rate of 50~100mL / min.

6. The method for preparing a biomass-based hard carbon material according to claim 1, characterized in that, The power supply for the Joule heat treatment in step 4 is a DC power supply with a current density of 10~20A / cm², a treatment temperature of 1500℃, and a treatment time of 20s.

7. The application of the biomass-based hard carbon material prepared according to claim 1 in the negative electrode of a sodium-ion battery, characterized in that, By mass percentage, 80-95% of the biomass-based hard carbon material, 3-10% of the conductive agent and 2-10% of the binder are mixed, a solvent is added to adjust the solid content of the slurry, and the mixture is coated on the surface of the metal current collector. After drying, a sodium-ion battery negative electrode sheet is obtained.

8. The application of a biomass-based hard carbon material according to claim 7 in the negative electrode of a sodium-ion battery, characterized in that, The conductive agent is superconducting carbon black, the binder is sodium carboxymethyl cellulose, the metal current collector is copper foil, the coating thickness is 50-200 μm, the drying temperature is 60-120°C, and the drying time is 6-24 h.

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