Preparation method and application of oak leaf-based hard carbon negative electrode material

Abstract

The invention relates to a preparation method and application of an oak leaf-based hard carbon negative electrode material, and the preparation method comprises the following steps: S1, taking a proper amount of oak leaves as a biomass raw material, sequentially carrying out mechanical crushing, grinding, ultrasonic cleaning and filtering, and then treating in a freeze dryer at-80 DEG C for 24 hours to obtain a dried oak leaf precursor; s2, mixing the oak leaf precursor with deionized water according to a mass ratio of 20: 80, putting the mixture into a reaction kettle with a Teflon lining, and carrying out hydrothermal reaction for 24 hours to obtain biochar; s3, the biochar is placed in a tubular furnace and heated to 1000 DEG C to 1500 DEG C under nitrogen protection for carbonization, the oak leaf-based hard carbon negative electrode material is obtained after carbonization, the specific surface area of the prepared hard carbon negative electrode material is 10 m / g to 120 m / g, and the average pore size is 3 nm to 15 nm. The method has the advantages of small mesopores, high uniformity, excellent pore structure, high specific surface area and the like.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a method for preparing and applying an oak leaf-based hard carbon anode material. Background Technology

[0002] Hard carbon, due to its amorphous structure, high defect concentration, difficulty in graphitization, and large interlayer spacing, is widely used as the anode in sodium-ion batteries. Hard carbon products with both high specific capacity and high initial efficiency command market prices exceeding 150,000 RMB per ton. Currently, the main methods for preparing hard carbon include chemical vapor deposition and high-temperature pyrolysis, with pyrolysis being safer, more stable, and suitable for mass production. Precursors available for pyrolysis include biomass, bitumen, and resin, with biomass being one of the best choices due to its environmental friendliness and economic viability. However, the precise distribution of pore structure and the consistency of performance are the biggest challenges for biomass hard carbon products, failing to meet the large-scale requirements of high-performance sodium batteries. Chinese patent (publication number CN119079975A) discloses a camphor leaf-based hard carbon anode material, its preparation method, and its application. The process includes: 1) drying and pulverizing camphor leaves extracted from camphor trees to obtain a powder; 2) heating the powder to 1400℃ under nitrogen or inert gas protection and holding for at least 2 hours to obtain a pyrolytic carbon material; and 3) immersing the pyrolytic carbon material in hydrochloric acid for at least 12 hours, then washing with water until neutral, and drying to obtain the camphor leaf-based hard carbon anode material. The technical problems are: firstly, the acid washing generates chemical waste that needs treatment, resulting in poor environmental performance; secondly, the carbonization temperature is fixed at 1400℃, preventing adjustments to the production process according to different application requirements, thus hindering its market prospects; and thirdly, the specific capacity and rate performance of the prepared hard carbon anode material need improvement. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an oak leaf-based hard carbon anode material with small mesopores, high uniformity, excellent pore structure, and high specific surface area. The preparation process of the oak leaf-based hard carbon anode material is simple, the cost is low, and the product quality is stable. When applied to sodium-ion battery anode materials, it can improve the main performance of sodium-ion batteries and enhance their rate performance and cycle performance.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention also provides a method for preparing an oak leaf-based hard carbon anode material, characterized by the following steps: S1: Take an appropriate amount of oak leaves as biomass raw material, and mechanically crush and grind them in sequence to crush the oak leaves into oak leaf particles of less than 1 mm; add the oak leaf particles to deionized water for ultrasonic cleaning, filter after cleaning, and then treat them in a freeze dryer at -80°C for 24 hours to obtain dried oak leaf precursor. S2: The dried oak leaf precursor was mixed with deionized water at a mass ratio of 20:80 and placed in a reaction vessel with a Teflon liner for hydrothermal reaction at a temperature of 180°C. The mixture was magnetically stirred during the hydrothermal reaction. The hydrothermal reaction lasted for 24 hours. The solid precipitate was then separated, washed three times with deionized water, and dried at 70°C to constant weight to obtain biochar. S3: The biochar is placed in a tube furnace and heated to 1000℃-1500℃ under nitrogen protection for carbonization for 2 hours, and then naturally cooled to room temperature to obtain oak leaf-based hard carbon anode material; the obtained oak leaf-based hard carbon anode material has a specific surface area of ​​10-120 m² / g and an average pore size of 3-15 nm.

[0005] As a preferred embodiment of the present invention, an oak leaf-based hard carbon anode material with a specific surface area of ​​50-100 m² / g and an average pore size of 5-10 nm is preferred.

[0006] Furthermore, the carbonization heating rate in step S3 is 5°C / min.

[0007] The oak leaf-based hard carbon anode material obtained by this invention is suitable as an anode material for sodium-ion batteries, and can effectively improve the rate performance and cycle life of sodium-ion batteries.

[0008] The preparation process of this invention is relatively environmentally friendly, especially in the hydrothermal pretreatment stage, which does not require a large amount of harmful chemical reagents, the reaction conditions are mild, and there is no need for a high-temperature environment or inert gas protection. Therefore, it is environmentally friendly and has the advantages of being environmentally friendly, having low energy consumption, and low cost.

[0009] The oak leaf precursor in this invention, after hydrothermal pretreatment and high-temperature carbonization, yields biomass hard carbon with a high specific surface area and uniform pore structure, which gives it excellent electrochemical performance, especially in energy storage devices such as supercapacitors and lithium-ion batteries.

[0010] The hydrothermal pretreatment and carbonization temperature in this preparation method can be adjusted according to specific needs, thereby controlling the pore structure, specific surface area, conductivity, and other properties of hard carbon, exhibiting high adjustability. By changing the hydrothermal pretreatment conditions or carbonization temperature, the performance of hard carbon can be precisely controlled to meet different application requirements.

[0011] In summary, the oak leaf-based hard carbon anode material prepared by this invention has the advantages of small mesopores, high uniformity, excellent pore structure, and high specific surface area. The preparation method of this oak leaf-based hard carbon anode material is simple, low-cost, and yields a product with stable quality. When applied to sodium-ion battery anode materials, it can improve the main performance characteristics of sodium-ion batteries, enhancing their rate performance and cycle performance. Attached Figure Description

[0012] Figure 1 This is a graph showing the relationship between the discharge specific capacity and current density of the half-cell negative electrode material prepared by the method of this invention. Figure 2 This is a graph showing the relationship between the specific capacity of a half-cell charge and the current density of the negative electrode material prepared by the method of this invention. Figure 3 This is a graph showing the relationship between the average reversible capacity and current density of the full cell containing the negative electrode material prepared by the method of this invention. Figure 4 This is a nitrogen adsorption-desorption curve of the negative electrode material prepared by the method of this invention; Figure 5 This is a curve showing the specific surface area and average pore size of the negative electrode material prepared by the method of this invention. Detailed Implementation

[0013] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0014] Example 1: Preparation method of oak leaf-based hard carbon anode material, mainly using the following steps: S1: Biomass pretreatment: Oak leaves are selected as biomass raw material. The particle size is reduced to less than 1 mm by mechanical crushing and grinding. The crushed biomass is ultrasonically cleaned in deionized water to remove surface impurities. After filtration and washing, it is freeze-dried at -80°C for 24 hours to obtain a dry precursor. S2: Hydrothermal Pretreatment: The freeze-dried biomass precursor was mixed with deionized water at a mass ratio of 20:80 and subjected to a hydrothermal reaction in a Teflon-lined container. During this process, the reactor was heated at 180°C for 24 hours under a sealed condition, and the uniformity of the reaction was ensured by continuous magnetic stirring. After the hydrothermal reaction was completed, the precipitate was separated and rinsed multiple times with deionized water to remove dissolved substances, resulting in a hydrothermally treated solid product. This product was then dried overnight at 70°C to remove residual moisture. S3: High-temperature carbonization: The dried biochar was placed in a tube furnace and carbonized at high temperature under a nitrogen protective atmosphere. The carbonization temperature was 1000°C, the carbonization time was 2 hours, the heating rate was controlled at 5°C / min, and then it was naturally cooled to room temperature to obtain the oak leaf-based hard carbon anode material HP1 (hydrothermal pre-carbonized).

[0015] Example 2: Preparation method of oak leaf-based hard carbon anode material, mainly using the following steps: S1: Biomass pretreatment: Oak leaves are selected as biomass raw material. The particle size is reduced to less than 1 mm by mechanical crushing and grinding. The crushed biomass is ultrasonically cleaned in deionized water to remove surface impurities. After filtration and washing, it is freeze-dried at -80°C for 24 hours to obtain a dry precursor. S2: Hydrothermal Pretreatment: The freeze-dried biomass precursor was mixed with deionized water at a mass ratio of 20:80 and subjected to a hydrothermal reaction in a Teflon-lined container. During this process, the reactor was heated at 180°C for 24 hours under a sealed condition, and the uniformity of the reaction was ensured by continuous magnetic stirring. After the hydrothermal reaction was completed, the precipitate was separated and rinsed multiple times with deionized water to remove dissolved substances, resulting in a hydrothermally treated solid product. This product was then dried overnight at 70°C to remove residual moisture. S3: High-temperature carbonization: The dried biochar was placed in a tube furnace and carbonized at high temperature under a nitrogen protective atmosphere. The carbonization temperature was 1300°C, the carbonization time was 2 hours, the heating rate was controlled at 5°C / min, and then it was naturally cooled to room temperature to obtain the oak leaf-based hard carbon anode material HP2.

[0016] Example 3: Preparation method of oak leaf-based hard carbon anode material, mainly using the following steps: S1: Biomass pretreatment: Oak leaves are selected as biomass raw material. The particle size is reduced to less than 1 mm by mechanical crushing and grinding. The crushed biomass is ultrasonically cleaned in deionized water to remove surface impurities. After filtration and washing, it is freeze-dried at -80°C for 24 hours to obtain a dry precursor. S2: Hydrothermal Pretreatment: The freeze-dried biomass precursor was mixed with deionized water at a mass ratio of 20:80 and subjected to a hydrothermal reaction in a Teflon-lined container. During this process, the reactor was heated at 180°C for 24 hours under a sealed condition, and the uniformity of the reaction was ensured by continuous magnetic stirring. After the hydrothermal reaction was completed, the precipitate was separated and rinsed multiple times with deionized water to remove dissolved substances, resulting in a hydrothermally treated solid product. This product was then dried overnight at 70°C to remove residual moisture. S3: High-temperature carbonization: The dried biochar was placed in a tube furnace and carbonized at high temperature under a nitrogen protective atmosphere. The carbonization temperature was 1500°C, the carbonization time was 2 hours, the heating rate was controlled at 5°C / min, and then it was naturally cooled to room temperature to obtain the oak leaf-based hard carbon anode material HP3.

[0017] Comparative Example 1: The preparation method of hard carbon products mainly adopts the following steps: S1: Biomass Pretreatment: Oak leaves were selected as the biomass raw material and their particle size was reduced to less than 1 mm through mechanical crushing and grinding. The crushed biomass was ultrasonically cleaned in deionized water to remove surface impurities, then filtered, washed, and treated in a freeze dryer at -80°C for 24 hours to obtain a dried precursor. S2: Anhydrous heat treatment step; S3: High-temperature carbonization: The freeze-dried biomass precursor is placed directly in a tube furnace and carbonized at high temperature under a nitrogen protective atmosphere. The carbonization temperature is 1000°C, the carbonization time is 2 hours, the heating rate is controlled at 5°C / min, and then it is naturally cooled to room temperature to obtain the hard carbon product DC1 (direct carbonized).

[0018] Comparative Example 2: The preparation method of hard carbon products mainly adopts the following steps: S1: Biomass Pretreatment: Oak leaves were selected as the biomass raw material and their particle size was reduced to less than 1 mm through mechanical crushing and grinding. The crushed biomass was ultrasonically cleaned in deionized water to remove surface impurities, then filtered, washed, and freeze-dried at -80°C for 24 hours to obtain a dried precursor. S2: Anhydrous heat treatment step; S3: High-temperature carbonization: The freeze-dried biomass precursor is placed directly in a tube furnace and carbonized at high temperature under a nitrogen protective atmosphere. The carbonization temperature is 1300°C, the carbonization time is 2 hours, the heating rate is controlled at 5°C / min, and then it is naturally cooled to room temperature to obtain the hard carbon product DC2.

[0019] Comparative Example 3: The preparation method of hard carbon products mainly adopts the following steps: S1: Biomass Pretreatment: Oak leaves were selected as the biomass raw material and their particle size was reduced to less than 1 mm through mechanical crushing and grinding. The crushed biomass was ultrasonically cleaned in deionized water to remove surface impurities, then filtered, washed, and freeze-dried at -80°C for 24 hours to obtain a dried precursor. S2: Anhydrous heat treatment step; S3: High-temperature carbonization: The freeze-dried biomass precursor is placed directly in a tube furnace and carbonized at high temperature under a nitrogen protective atmosphere. The carbonization temperature is 1500°C, the carbonization time is 2 hours, the heating rate is controlled at 5°C / min, and then it is naturally cooled to room temperature to obtain the hard carbon product DC3.

[0020] Material structure characterization experiment The morphology of the samples was studied using scanning electron microscopy (SEM). High-resolution transmission electron microscopy images were acquired by TEM at 200 kV. Nitrogen adsorption analysis was performed at 77 K. The specific surface area and pore size distribution of the products were obtained using the Brunauer-Emmett-Teller (BET) method and nonlocal density functional theory (NLDFT) analysis. The nitrogen adsorption-desorption test results for each sample are shown in [Figure number missing]. Figure 4 .

[0021] The product HP1 obtained in Example 1 had a specific surface area of ​​114.1 m² / g and an average pore size of 3.9 nm. The product HP2 obtained in Example 2 had a specific surface area of ​​61.5 m² / g and an average pore size of 5.8 nm. The product HP3 obtained in Example 3 had a specific surface area of ​​15.4 m² / g and an average pore size of 11.3 nm. The product DC1 obtained in Comparative Example 1 had a specific surface area of ​​34.5 m² / g and an average pore size of approximately 4.9 nm. The product DC2 obtained in Comparative Example 2 had a specific surface area of ​​10.93 m² / g and an average pore size of approximately 11.3 nm. The product DC3 obtained in Comparative Example 3 had a specific surface area of ​​4.13 m² / g and an average pore size of approximately 16.9 nm.

[0022] The specific surface area (S) of HP1, HP2, and HP3 products was used to determine the specific surface area (S). BET ) and average aperture (P V The data were fitted using a double exponential function, and the fitting function was... ,in = 381.1202, =-188.035, = 3.14464, = 128.035, = 3.14464, substituting and rearranging, we get S BET =381.1202-60.000 The results show that R²(COD)≈0.99857 and Reduced Chi-Sqr≈4.29479. Analysis of variance reveals a high F-value of 1217.886 and a very small p-value (<0.0001), indicating that the model has a strong explanatory power for the experimental data and excellent fit quality. This function can be used to inversely calculate the required carbonization temperature based on the specific surface area and average pore size requirements of different application scenarios.

[0023] Battery performance test experiment 1. Half-cell performance test The half-cells were assembled using CR2032 coin cell casings. The working anode was prepared using products from Examples 1-3 (HP1, HP2, HP3) and Comparative Examples 1-3 (DC1, DC2, DC3), mixed with carboxymethyl cellulose (CMC) and superphosphate (SPF) at a mass ratio of 8:1:1, and then coated onto aluminum foil. The electrode loading mass was 0.8-1.2 mg cm⁻², and the thickness was ±0.0035 mm. Half-cells were prepared for these samples, numbered HP1, HP2, HP3, DC1, DC2, and DC3, respectively. The counter electrode and reference electrode were both sodium metal sheets. The separator was a glass fiber separator. The electrolyte was 1 M NaPF6 dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1, volume ratio), with 5% fluoroethylene carbonate (FEC) added. All cells were assembled in a glove box (humidity < 1%). The assembled batteries were subjected to constant current charge-discharge (GCD) tests on a battery tester with a voltage range of 0.01–2.5 V and current densities of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C. Specific capacity, initial coulombic efficiency, and long-term cycle stability were recorded, and rate performance and cycle performance were analyzed.

[0024] 2. Full Battery Performance Testing The full cells were prepared using the products obtained in Examples 1-3 (HP1, HP2, HP3) and Comparative Examples 1-3 (DC1, DC2, DC3) as the negative electrode and Na3V2(PO4)3 (NVP) as the positive electrode. The positive electrode was prepared by coating aluminum foil with a mixture of NVP powder, PVDF binder and super P in a mass ratio of 6:2:2 and drying it overnight in a vacuum environment at 120°C. The sample numbers were HP1, HP2, HP3, DC1, DC2, and DC3, respectively.

[0025] The electrolyte was 1 M NaPF6 dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1, volume ratio), with 5% FEC added. The separator was a glass fiber separator. The positive and negative electrode capacity ratio was 1.1. After the battery was assembled in a glove box, constant current charge-discharge tests were performed within a voltage range of 1.5–3.9 V, and different current densities (60, 150, 300, 600, 1500, and 3000 mAhg) were recorded. -1 The specific capacity, rate performance, and initial coulombic efficiency were measured under these conditions, and 200 long-cycle stability tests were conducted to record the capacity retention.

[0026] Table 1. Parameters of GCD curve at 0.1C for half-cell

[0027] Table 2 Half-cell rate performance test table

[0028] Table 3 Full Battery Test Parameters

[0029] Table 4 Average pore size and specific surface area

[0030] As can be seen from Table 1, the HP2 half-cell exhibits the highest capacity retention (97%) after 100 cycles and good initial coulombic efficiency (88%) at 0.1C. From Table 2 and Figure 1 As can be seen, the HP2 half-cell has the highest discharge specific capacity at high rate current density (>1C); From Table 2 and Figure 2 As can be seen, the HP2 half-cell has good charge capacity at high rate current density (>1C); As can be seen from Table 2, the HP2 half-cell has the best rate performance (72.5% at 10C). From Table 3 and Figure 3 As can be seen, the HP2 full cell has the highest reversible capacity at high rate current density (>300 mAh / g); From Table 4 and Figure 5 As can be seen, HP2 material has a moderate average pore size and specific surface area.

[0031] As can be seen from the above examples and comparative examples, this invention achieves a highly efficient, low-cost, and environmentally friendly method for preparing hard carbon materials by introducing hydrothermal pretreatment and high-temperature carbonization processes. Compared with the comparative sample without hydrothermal treatment, the example samples have a higher specific surface area and a smaller average pore size, correspondingly exhibiting higher specific capacity, rate performance, and better cycle stability. This demonstrates that hydrothermal pretreatment can optimize the pore structure and specific surface area of ​​the material, providing significantly superior electrochemical performance. Among them, the HP2 sample has a specific surface area and average pore size within the preferred range, and performs best in terms of initial discharge specific capacity, 10C rate performance, and cycle stability, proving that a suitable carbonization temperature (1300°C) further enhances conductivity and material performance. The oak leaf-based hard carbon anode material prepared by this invention provides sodium-ion battery products with high performance, long lifespan, and low cost as core competitive advantages. Through a synergistic process of hydrothermal pretreatment and high-temperature carbonization, the material possesses a specific surface area of ​​10-120 m² / g and an average pore size of 3-15 nm, with a preferred specific surface area of ​​50-100 m² / g and an average pore size of 5-10 nm. The micropores precisely adsorb sodium ions, enhancing reversible capacity (up to 316 mAh / g at 0.1C), achieving a high initial efficiency of 88% and ultra-fast charge / discharge performance at 10C (capacity retention >72%). Furthermore, the battery retains over 90% of its capacity after 3000 cycles, significantly extending product lifespan. Simultaneously, the material utilizes renewable oak leaf resources, employing a green and low-carbon process (free from strong acid / alkali pollution), and its naturally low impurity characteristics ensure high battery safety. Moreover, this invention offers strong process controllability; by adjusting the hydrothermal and carbonization conditions, it can meet various energy storage needs and is suitable for various energy storage devices such as sodium-ion batteries, lithium-ion batteries, and supercapacitors. This technological breakthrough has enabled sodium-ion batteries to achieve comprehensive optimization in key indicators such as energy density, fast charging capability, and cycle stability, providing a negative electrode solution with both high cost-effectiveness and scalability potential for power batteries, grid energy storage, and consumer electronics.

[0032] The present invention has been described in detail with reference to the above embodiments regarding its methods, steps, and effects; however, the scope of protection of the present invention is not limited to the specific embodiments described above. Any modifications, substitutions, improvements, or equivalent solutions based on the basic principles of the present invention and employing the same or similar technical means to achieve the same or similar technical effects should be considered within the scope of protection of the present invention.

[0033] The claims of this invention shall be governed by the appended claims. Technical features and parameters mentioned in the specification, unless expressly defined in the claims, shall not be deemed to limit the scope of protection of this invention.

Claims

1. A method for preparing an oak leaf-based hard carbon anode material, characterized in that... The following steps are adopted: S1. Take an appropriate amount of oak leaves as biomass raw material, and mechanically crush and grind them in sequence to crush the oak leaves into oak leaf particles of less than 1 mm; add the oak leaf particles to deionized water for ultrasonic cleaning, filter after cleaning, and then treat them in a freeze dryer at -80°C for 24 hours to obtain dried oak leaf precursor. S2. The dried oak leaf precursor was mixed with deionized water at a mass ratio of 20:80 and placed in a reaction vessel with a Teflon liner for hydrothermal reaction at a temperature of 180°C. The mixture was magnetically stirred during the hydrothermal reaction. The hydrothermal reaction lasted for 24 hours. The solid precipitate was then separated, washed three times with deionized water, and dried at 70°C to constant weight to obtain biochar. S3. The biochar is placed in a tube furnace and heated to 1000℃-1500℃ under nitrogen protection for carbonization for 2 hours, and then naturally cooled to room temperature to obtain oak leaf-based hard carbon anode material; the oak leaf-based hard carbon anode material has a specific surface area of ​​10-120 m² / g and an average pore size of 3-15 nm.

2. The method for preparing an oak leaf-based hard carbon anode material according to claim 1, characterized in that: The oak leaf-based hard carbon anode material has a specific surface area of ​​50-100 m² / g and an average pore size of 5-10 nm.

3. The method for preparing an oak leaf-based hard carbon anode material according to claim 1, characterized in that: In step S3, the carbonization heating rate is 5℃ / min.

4. The application of the oak leaf-based hard carbon anode material prepared according to the preparation method of claim 1 or 3 in sodium-ion batteries, characterized in that: As a negative electrode material for sodium-ion batteries.

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