An oak-based hard carbon anode material, its preparation method and application

Abstract

This invention discloses an oak-based hard carbon anode material, its preparation method, and its application. The preparation method includes the following steps: ball milling and mixing oak powder with a composite metal salt containing zinc chloride and copper chloride to obtain a precursor mixture; subjecting the precursor mixture to a primary carbonization treatment to obtain a primary carbonization product; acid washing the primary carbonization product to remove impurities; and subjecting the acid-washed product to a secondary carbonization treatment under a protective atmosphere, followed by cooling to obtain the oak-based hard carbon anode material. This invention achieves synergistic optimization of pore structure, conductivity, and energy storage activity through the synergistic catalytic and pore-forming effects of specific composite metal salts, combined with stepwise carbonization and acid washing purification processes. The resulting oak-based hard carbon anode material exhibits high specific capacity, excellent initial coulombic efficiency, and cycle stability. Furthermore, the raw materials are widely available, low-cost, and the process is highly controllable, making it suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to an oak-based hard carbon anode material, its preparation method, and its application. Background Technology

[0002] With the transformation of the global energy structure and the rapid development of electric vehicles and large-scale energy storage, the long-term application of lithium-ion batteries faces challenges due to the limited and uneven distribution of lithium resources and the continuous rise in costs. Sodium-ion batteries, with their abundant sodium resources, low cost, and similar working principle to lithium-ion batteries, are considered one of the most promising next-generation electrochemical energy storage systems.

[0003] The anode material is a key component that determines the performance of sodium-ion batteries. Hard carbon materials, due to their resistance to graphitization even at temperatures above 2500℃ and their unique internal pore structure and interlayer spacing, are very suitable for the storage and transport of sodium ions, thus becoming the preferred anode material for sodium-ion batteries.

[0004] Currently, precursors for preparing hard carbon anode materials are mainly divided into fossil fuel-based (such as asphalt and petroleum coke) and polymer-based (such as phenolic resin and polyacrylonitrile). However, fossil fuel-based precursors suffer from problems such as non-renewability and severe environmental pollution; polymer-based precursors face challenges such as complex synthesis processes, excessively high post-processing temperatures, and high costs, limiting the commercial application of sodium-ion batteries in large-scale energy storage. Chinese Patent Publication No. CN114804068A discloses a method for preparing hard carbon anode materials by vapor deposition, which uses waste tires as a carbon source. Although it achieves good electrochemical performance, it suffers from drawbacks such as cumbersome process steps and high post-processing temperatures (1500–2200℃).

[0005] Biomass materials, due to their wide availability, low cost, renewability, and environmental friendliness, have become a highly promising alternative precursor. Oak, a typical hardwood resource, produces wood flour primarily composed of cellulose, hemicellulose, and lignin. Cellulose (approximately 40-45%) provides regular carbon skeleton units, hemicellulose (approximately 20-30%) readily decomposes in the early stages of pyrolysis and induces initial pore formation, while lignin, rich in aromatic structures (approximately 20-30%), is the key source for constructing high carbon yields and graphite-like microcrystalline domains. This natural "three-component synergy" structure makes oak flour an excellent biomass precursor for preparing hard carbon electrode materials.

[0006] However, oak wood powder generally contains a high content of inorganic mineral ash (such as K, Ca, Mg, Si, etc.), and its surface is rich in oxygen-containing functional groups such as hydroxyl, carboxyl, and ether bonds. While these characteristics endow it with good chemical reactivity, they can also trigger non-uniform cracking and disordered catalytic effects during carbonization, leading to unstable hard carbon microcrystalline structure and uncontrolled pore size distribution, which in turn affects electrochemical performance.

[0007] Therefore, how to effectively control the oak powder precursor through a simple process to prepare high-performance hard carbon anode materials with high specific capacity, high initial coulombic efficiency and excellent cycle stability at low cost is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides an oak-based hard carbon anode material, its preparation method, and its application. The method involves introducing a metal salt impregnation pretreatment before carbonization and acid washing after initial carbonization to achieve precise control over the chemical composition and pyrolysis path of the wood flour. In the later carbonization stage, the final carbonization temperature is specifically adjusted to achieve synergistic optimization between pore structure, conductivity, and energy storage activity. The resulting oak-based hard carbon anode material exhibits high specific capacity, excellent initial coulombic efficiency, and cycle stability. Furthermore, the raw materials are widely available, inexpensive, and the process is highly controllable, making it suitable for industrial production.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing an oak-based hard carbon anode material, comprising the following steps: S1. The oak wood powder precursor is ball-milled and mixed with the composite metal salt to obtain a precursor mixture; the composite metal salt contains zinc chloride and copper chloride. S2. The precursor mixture is subjected to primary carbonization treatment to obtain the primary carbonization product. S3. The initial carbonization product is acid-washed to obtain the acid-washed product. After acid washing, it is washed with deionized water until the pH value is 7. The washed carbon material is dried in an oven for 24 hours at a temperature of 60℃. S4. Under a protective atmosphere, the acid-washed product is subjected to a secondary carbonization treatment, and after cooling, oak-based hard carbon anode material is obtained.

[0010] The above technical solution is adopted: First, this invention introduces a ZnCl2-CuCl2 composite metal salt system as a structure inducer. During heat treatment, the two metal salts play distinctly different but synergistic roles: ZnCl2 is a strong Lewis acid. In the early stage of carbonization, it can undergo dehydration, cross-linking and complexation reactions with the hydroxyl groups on cellulose and hemicellulose in oak powder, significantly changing the pyrolysis path of the precursor. Its main functions are: (1) Activating pore formation: At high temperature, ZnCl2 and its derivatives occupy space as templates. After being washed away, they leave behind a rich pore structure, especially micropores; (2) Promoting aromatization: ZnCl2 can catalyze the aromatization and cyclization reactions of carbon skeletons, which helps to form short-range ordered graphite-like microcrystalline carbon skeleton structures and improve the conductivity of materials.

[0011] CuCl2 exhibits a weak graphitization catalytic effect on carbon layers at high temperatures, promoting the rearrangement of amorphous carbon layers towards a more ordered direction and forming a more regular carbon layer structure in local areas, which is beneficial for improving electron transport rates. The combined use of ZnCl2 and CuCl2 forms a synergistic "activation-etching-reconstruction" mechanism. ZnCl2 is primarily responsible for constructing a well-developed microporous network to provide sodium storage active sites, while CuCl2 focuses on optimizing the carbon layer arrangement and improving local conductivity. The synergistic effect of both significantly expands the pore network and optimizes the carbon layer stacking pattern, thereby constructing a hard carbon framework with both high specific surface area and good conductivity—an effect that cannot be achieved by single metal salt treatment.

[0012] Secondly, this invention employs a stepwise carbonization process. The initial carbonization is carried out at a relatively low temperature (500-700℃), allowing the oak wood powder to essentially complete pyrolysis and the initial formation of the carbon skeleton, while simultaneously decomposing the metal salts and allowing them to fully interact with the carbon skeleton. The subsequent acid washing step, on the one hand, removes ash and inorganic ions; the acid dissolves alkali metal and alkaline earth metal impurities in the wood powder, significantly weakening their heterogeneous catalytic effect during carbonization and improving the uniformity of the carbon skeleton structure from the source. On the other hand, it can adjust the thermal stability of the components; the acidic environment can selectively hydrolyze hemicellulose and some lignin side chains, making the pyrolysis process more controllable. It can also introduce functional groups, such as nitric acid treatment, which can introduce functional groups such as –COOH and –NO2, enhancing the reactivity of the precursor and promoting subsequent carbon layer rearrangement. After acid treatment, the decomposition temperature range, carbon yield, and volatility behavior of the wood powder are significantly altered, thereby directly affecting the microcrystalline size and pore structure of the final hard carbon. After acid washing, the inorganic impurities in the wood flour precursor are significantly reduced, and the pyrolysis behavior tends to be more consistent, which is conducive to the formation of a typical hard carbon microstructure in which short-range order and long-range disorder coexist.

[0013] Due to the metal salt impregnation and acid pickling processes, the subsequent carbonization and activation stages can be improved by appropriately reducing the heating rate, shortening the high-temperature holding time, or weakening the secondary activation intensity, thus avoiding pore wall collapse and conductivity loss caused by excessive etching. Finally, a secondary carbonization at a higher temperature (900-1100℃) further repairs defects, adjusts crystallite size and interlayer spacing on the basis of a pure carbon framework, thereby precisely controlling the final hard carbon structure and improving the material's electrochemical stability and specific capacity. This step-by-step treatment avoids the adverse effects of impurities on the carbon structure and the collapse of the pore structure that would occur with simultaneous high-temperature processing.

[0014] Further, in step S1, the molar ratio of zinc chloride to copper chloride in the composite metal salt is 1:1.

[0015] Furthermore, in step S1, the mass ratio of oak wood powder to composite metal salt is 1:1.

[0016] Controlling the amount of metal salt used is crucial: too low a concentration results in insufficient activation and catalysis; too high a concentration can lead to over-etching, damaging the carbon skeleton structure and consequently reducing electrochemical performance. In this application, oak wood powder and composite metal salt were mixed in a ball mill at mass ratios of 1:2, 1:1, and 2:1, followed by preliminary carbonization, acid washing, and secondary carbonization. The resulting carbon material was then fabricated into electrode sheets and assembled into half-cells. Its electrochemical performance was tested and analyzed. The final experimental results showed that the carbon material with the best electrochemical performance (specific capacity of 334.92 mAh / g) was obtained when the mass ratio of composite metal salt to wood powder was 1:1.

[0017] Further, in step S2, the initial carbonization temperature is 500–700°C, the heating rate is 2–3°C / min, and the holding time is 1–3 hours. Preferably, the initial carbonization is carried out in a box furnace, with a carbonization temperature of 600°C, a heating rate of 2.5°C / min, and a holding time of 2 hours. The atmosphere for the initial carbonization can be a natural atmosphere or an inert protective atmosphere; from a cost perspective, it is preferred to carry out the process in a box furnace under a natural atmosphere.

[0018] Furthermore, in step S3, the acid solution used in the pickling process is hydrochloric acid, and the concentration of hydrochloric acid is 2-3 mol / L.

[0019] This application employs acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, and nitric acid to acid-wash the initially carbonized carbon materials, aiming to compare the effects of different acids on ash removal and thus screen the optimal acid-washing system. Experimental results show that, under the same treatment conditions, hydrochloric acid has the most significant ash removal effect. Further concentration gradient experiments with hydrochloric acid were conducted to optimize the acid-washing process parameters. It was found that when the hydrochloric acid concentration was increased from 1 mol / L to 2 mol / L, the ash content decreased significantly; further increasing the concentration to 3 mol / L resulted in limited ash reduction, while at 4 mol / L, the ash content slightly increased. Considering both ash removal efficiency and acid consumption cost, a hydrochloric acid concentration of 2–3 mol / L ensures both good ash removal efficiency and economic efficiency, thus determining it as the optimal acid-washing condition. The preferred acid-washing temperature is 60℃, and the time is 2 h.

[0020] Furthermore, in step S3, during the pickling process, the liquid-to-solid ratio of the acid solution to the carbon material is 0.8L to 1.2L: 5g.

[0021] Furthermore, in step S4, the secondary carbonization treatment temperature is 900–1100℃, the heating rate is 1–3℃ / min, the holding time is 1–3h, and then the temperature is gradually reduced to room temperature at a rate of 2–3℃ / min.

[0022] In this application, a gradient screening of secondary carbonization temperatures was conducted. Test results show that performance is best at secondary carbonization temperatures of 900–1100℃, preferably 1100℃. The holding time was adjusted mainly based on the precursor processing technology. After mixing the metal salt, the holding time was preferably extended to 2–3 hours to ensure sufficient volatilization of the metal salt and etching of a dense porous structure in the carbon material. Temperature has little effect on the closed-cell formation system; therefore, a conventional heating rate range of 1–3℃ / min is acceptable. Typically, to improve carbonization efficiency, a heating rate of 2–3℃ / min is preferred.

[0023] In a second aspect, the present invention provides an oak-based hard carbon anode material, which is prepared by the above-described preparation method.

[0024] A third aspect of the present invention provides an application of the above-mentioned oak-based hard carbon anode material, wherein the oak-based hard carbon anode material is used to prepare a sodium-ion battery anode sheet.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces a composite metal salt composed of ZnCl2 and CuCl2 as a structure inducer. ZnCl2 and CuCl2 form a synergistic mechanism of "activation-etching-reconstruction". ZnCl2 is mainly responsible for building a well-developed microporous network to provide active sites for sodium storage, while CuCl2 focuses on optimizing the carbon layer arrangement and improving local conductivity. The two work together to significantly expand the pore network and optimize the carbon layer stacking mode, thereby constructing a hard carbon framework with both high specific surface area and good conductivity, which is an effect that cannot be achieved by single metal salt treatment. Electrochemical test results show that the hard carbon material prepared by using this composite metal salt system has a reversible specific capacity of more than 364 mAh / g, and the initial coulombic efficiency and cycle stability are significantly improved.

[0026] (2) This invention also adopts a “primary carbonization-acid washing purification-secondary carbonization” process. Through step-by-step process design, it solves the problems of many impurities in biomass precursors and uncontrollable pyrolysis process. The primary carbonization is completed at a relatively low temperature, so that the oak powder is basically pyrolyzed and forms an initial carbon skeleton. At the same time, the metal salts fully penetrate and play a role. The subsequent acid washing step not only efficiently removes the original ash impurities such as alkali metals and alkaline earth metals in the carbon material, but also eliminates the negative heterogeneous catalytic effect of impurities in subsequent high-temperature treatment from the source. At the same time, the acid washing process selectively removes the metal salt derivatives occupying the pores, opens the blocked pores, and functionalizes the carbon surface, providing a pure and more active carbon substrate for secondary carbonization. By performing secondary carbonization at higher temperatures (900-1100℃) on a pure carbon skeleton, the microcrystal size, carbon layer spacing, and defect concentration can be precisely controlled under ideal conditions without interference from impurities. This repairs structural defects that may occur during the initial carbonization and acid washing process, making the carbon layer arrangement more stable and orderly, and avoiding the collapse of pore structure and excessive graphitization caused by impurities during high-temperature co-processing.

[0027] (3) This invention uses oak wood powder, a forestry waste, as a precursor. It is widely available, inexpensive, and renewable, which aligns with the green and sustainable development strategy and provides a new approach for the high-value utilization of biomass waste. In addition, the ball milling, carbonization, and acid washing processes used in this invention are all conventional operation units in the chemical industry, with low equipment requirements and controllable parameters, making them suitable for large-scale production. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 This embodiment provides a method for preparing an oak-based hard carbon anode material, including the following steps: (1) Precursor mixing: Weigh 10 g of dried oak powder and 10 g of composite metal salt (SA, which is made by grinding CuCl2 and ZnCl2 in a molar ratio of 1:1) (i.e., the mass ratio of oak powder to composite metal salt is 1:1). Place the two together in a ball mill and mix at a speed of 400 r / min for 3 h. After ball milling, the sample is sieved through a 100-mesh sieve to obtain a fully and uniformly dispersed precursor mixture.

[0030] (2) Primary carbonization: The precursor mixture is placed in a box furnace and primary carbonized under natural atmosphere. The carbonization procedure is as follows: the temperature is increased to 600 ℃ at a rate of 2.5 ℃ / min and held at this temperature for 2 h, then naturally cooled to room temperature, and the primary carbonized product is taken out.

[0031] (3) Acid washing treatment: The initial carbonization product was immersed in a 2 mol / L hydrochloric acid solution with a liquid-solid ratio of 1 L: 5 g. The mixture was stirred in a 60 ℃ constant temperature water bath for 2 h. After acid washing, the carbon was filtered and repeatedly washed with deionized water until the pH of the filtrate was close to neutral. Then it was dried in an oven at 80 ℃.

[0032] (4) Secondary carbonization: The dried pickled carbon material is placed in a tube furnace and high-purity argon is introduced as a protective atmosphere. The carbonization procedure is as follows: the temperature is raised to 1100 ℃ at a rate of 2.5 ℃ / min and held at this temperature for 2 h, and then cooled to room temperature at a rate of 3 ℃ / min. The sample is then taken out to obtain the oak-based hard carbon anode material.

[0033] Example 2 This embodiment is basically the same as embodiment 1, except that: in step (2), the amount of oak powder used is 10 g and the amount of composite metal salt used is 20 g (that is, the mass ratio of oak powder to composite metal salt is 1:2).

[0034] Example 3 This embodiment is basically the same as embodiment 1, except that: in step (2), the amount of oak powder used is 10 g and the amount of composite metal salt is 5 g (that is, the mass ratio of oak powder to composite metal salt is 2:1).

[0035] Example 4 This embodiment is basically the same as embodiment 1, except that the initial carbonization temperature in step (3) is 500 ℃.

[0036] Example 5 This embodiment is basically the same as that of embodiment 1, except that the initial carbonization temperature in step (3) is 700 ℃.

[0037] Example 6 This embodiment is basically the same as embodiment 1, except that the secondary carbonization temperature in step (5) is 800 ℃.

[0038] Example 7 This embodiment is basically the same as embodiment 1, except that the secondary carbonization temperature in step (5) is 900 ℃.

[0039] Example 8 This embodiment is basically the same as embodiment 1, except that the secondary carbonization temperature in step (5) is 1000 ℃.

[0040] Example 9 This embodiment is basically the same as embodiment 1, except that the secondary carbonization temperature in step (5) is 1200 ℃.

[0041] Comparative Example 1 This comparative example is a comparative test example of Example 1, which is basically the same as Example 1, except that the metal salt in step (2) is a single component CuCl2.

[0042] Comparative Example 2 This comparative example is a comparative test example of Example 1, which is basically the same as Example 1, except that the metal salt in step (2) is a single component ZnCl2.

[0043] Comparative Examples 3-7 Screening test for the optimal pickling system: The carbon material after initial carbonization in Example 1 was subjected to acid washing treatment using acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, and nitric acid, respectively.

[0044] The acid washing process was as follows: The initial carbonization product from Example 1 was divided into five equal portions, which were then immersed in 1 mol / L solutions of acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, and nitric acid, respectively. The liquid-to-solid ratio of the acid solution to the carbon material was set at 1 L: 5 g. The mixture was stirred and reacted in a 60°C constant temperature water bath for 2 hours. After acid washing, the carbon material was filtered and repeatedly washed with deionized water until the pH of the filtrate was close to neutral. Subsequently, it was dried in an oven at 80°C. The ash content in the samples was then determined according to the method specified in the national standard GB / T 212-2008. The test results are shown in Table 1.

[0045] Table 1 sample Ash content in the treated charcoal sample Comparative Example 3 (Acetic Acid) 2.716 Comparative Example 4 (oxalic acid) 2.603 Comparative Example 5 (hydrochloric acid) 2.098 Example 6 (Sulfuric Acid) 2.107 Example 7 (Nitric Acid) 2.119 As shown in Table 1, under the same treatment conditions, hydrochloric acid has the most significant effect on removing ash from the carbon material.

[0046] Comparative Examples 8-11 Concentration gradient experiment of hydrochloric acid washing: The carbon material after initial carbonization in Example 1 was subjected to acid washing treatment using hydrochloric acid solutions with concentrations of 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L, respectively.

[0047] The acid washing process was as follows: The initial carbonization product from Example 1 was divided into four equal parts and immersed in hydrochloric acid solutions with concentrations of 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L, respectively. The liquid-to-solid ratio of the acid solution to the carbon material was set at 1 L: 5 g. The mixture was stirred and reacted in a 60°C constant temperature water bath for 2 hours. After acid washing, the carbon material was filtered and repeatedly washed with deionized water until the pH of the filtrate was close to neutral. Then, it was dried in an oven at 80°C. Subsequently, the ash content in the samples was determined according to the method specified in the national standard GB / T 212-2008. The test results are shown in Table 2.

[0048] Table 2 sample Ash content in the treated charcoal sample Comparative Example 8 2.098% Comparative Example 9 0.95% Comparative Example 10 0.88% Comparative Example 11 0.92% The test results in Table 2 show that when the hydrochloric acid concentration is increased from 1 mol / L to 2 mol / L, the ash content decreases significantly; further increasing the concentration to 3 mol / L results in a limited reduction in ash content, while the ash content slightly increases at 3 mol / L. Considering both the ash removal effect and acid consumption cost, a hydrochloric acid concentration of 2–3 mol / L can ensure good ash removal while maintaining economic efficiency, and the optimal pickling condition is determined to be 2 mol / L hydrochloric acid.

[0049] Electrochemical performance testing: The hard carbon materials obtained in the above embodiments (1-11) and comparative examples 1 and 2 were mixed with conductive agent Super P and binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added and ground into a uniform slurry. This slurry was coated onto an aluminum foil current collector, and after vacuum drying, rolling, and cutting, a working electrode was formed. Using a sodium metal sheet as the counter electrode and reference electrode, a glass fiber membrane as the separator, and a 1 mol / L NaPF6 solution of ethylene carbonate (EC) / diethyl carbonate (DEC) (volume ratio 1:1) as the electrolyte, a CR2032 coin cell was assembled in an argon-filled glove box.

[0050] Constant current charge-discharge tests were performed using a battery testing system, with a voltage window of 0.01-2.5 V (vs. Na⁺ / Na).

[0051] Specific capacity test: The test was conducted at a current density of 0.1C (1C=300 mA / g), and the mAh / g was calculated based on the discharge capacity and the mass of active material.

[0052] First Coulomb Efficiency (ICE) Test: Calculated based on the first charge / discharge specific capacity, the formula is: ICE = (first charge specific capacity / first discharge specific capacity) × 100%, used to assess irreversible capacity loss.

[0053] Cyclic performance testing: 500 charge-discharge cycles were performed at a current density of 1C to calculate the capacity retention rate and evaluate the structural stability through the capacity retention rate.

[0054] Rate performance testing: Capacity decay and recovery capabilities are tested using a stepped rate (e.g., from 0.1C to 2C).

[0055] The test results are shown in Table 3.

[0056] Table 3 sample 0.1C reversible specific capacity (mAh / g) First Coulomb Efficiency (%) 500-cycle capacity retention rate (%) Rate performance (0.1C, %) Example 1 334.92 88.72 87 75 Example 2 305.83 76.63 84 67 Example 3 310.12 81.95 85 72 Example 4 298.53 78.84 87 72 Example 5 288.67 81.76 87 73 Example 6 276.51 76.54 87 75 Example 7 287.09 84.31 86 69 Example 8 300.17 79.89 87 78 Example 9 315.15 67.68 85 64 Comparative Example 1 285.67 82.78 93 68 Comparative Example 2 300.21 79.57 87 69 As can be seen from the comparison of the test results of Example 1 and Comparative Examples 1 and 2 in Table 3, the present invention significantly improves the specific capacity, initial coulombic efficiency and cycle stability of hard carbon materials by introducing ZnCl2-CuCl2 composite metal salt, which fully demonstrates that there is a significant synergistic effect between ZnCl2 and CuCl2.

[0057] Comparison of the test results of Examples 1-3 shows that there is an optimal range for the amount of both in the composite metal salt. When the ratio of composite metal salt to oak powder is 1:1, the electrochemical performance of the prepared sample is the best.

[0058] A comparison of the test results in Examples 1 and 4 and 5 shows that the initial carbonization temperature has an impact on the performance of the samples. When the initial carbonization temperature is set to 600℃, the electrochemical performance of the samples is optimal.

[0059] A comparison of the test results in Examples 1 and 6-9 shows that the secondary carbonization temperature has a significant impact on the sample performance. Preferably, the secondary carbonization temperature is 900–1100℃. More preferably, under the conditions of 1100℃ and 2.5℃ / min, the carbon material achieves the optimal balance between microcrystalline structure order and porosity, thus exhibiting the best electrochemical performance.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an oak-based hard carbon anode material, characterized in that, Includes the following steps: S1. The oak wood powder precursor is ball-milled and mixed with the composite metal salt to obtain a precursor mixture; the composite metal salt contains zinc chloride and copper chloride. S2. The precursor mixture is subjected to primary carbonization treatment to obtain the primary carbonization product. S3. The initial carbonization product is subjected to acid washing treatment to obtain the acid-washed product; S4. Under a protective atmosphere, the acid-washed product is subjected to a secondary carbonization treatment, and after cooling, oak-based hard carbon anode material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of zinc chloride to copper chloride in the composite metal salt is 1:

1.

3. The preparation method according to claim 2, characterized in that, In step S1, the mass ratio of oak wood powder to composite metal salt is 1:

1.

4. The preparation method according to claim 1, characterized in that, In step S2, the initial carbonization temperature is 500–700℃, the heating rate is 2–3℃ / min, and the holding time is 1–3h.

5. The preparation method according to claim 1, characterized in that, In step S3, the acid used in the pickling process is hydrochloric acid, and the concentration of hydrochloric acid is 2-3 mol / L.

6. The preparation method according to claim 5, characterized in that, In step S3, during the pickling process, the liquid-to-solid ratio of acid solution to carbon material is 0.8L to 1.2L: 5g.

7. The preparation method according to claim 1, characterized in that, In step S4, the secondary carbonization treatment temperature is 900-1100℃, the heating rate is 1-3℃ / min, the holding time is 1-3h, and then the temperature is gradually reduced to room temperature at a rate of 2-3℃ / min.

8. An oak-based hard carbon anode material, characterized in that, It is prepared by any one of claims 1-7.

9. The application of the oak-based hard carbon anode material as described in claim 8, characterized in that, The oak-based hard carbon anode material is used to prepare anode sheets for sodium-ion batteries.