Preparation method of sodium ion battery hard carbon negative electrode material

Abstract

The invention relates to a preparation method of a sodium ion battery hard carbon negative electrode material, which comprises the following steps: preparing graphene oxide-containing phenolic sol, curing graphene oxide-containing phenolic gel, and curing the graphene oxide-containing phenolic sol in a water bath kettle at 50 DEG C for 24-48 hours to change the graphene oxide-containing phenolic sol into graphene oxide-containing phenolic gel; pre-carbonization: putting the graphene oxide-containing phenolic aldehyde gel into a tubular furnace, vacuumizing, filling argon or nitrogen into the tubular furnace, heating to 700-1000 DEG C at a heating speed of 2.0-5.0 DEG C / min, pre-carbonizing for 2-5 hours, cooling to room temperature, and grinding and crushing a sample; and performing high-temperature carbonization, namely putting the powdery hard carbon precursor into a tubular furnace, vacuumizing, filling argon or nitrogen into the tubular furnace, heating to 1100-1500 DEG C at a heating speed of 2.0-5.0 DEG C / min, and performing high-temperature carbonization to obtain the hard carbon negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a method for preparing a hard carbon anode material for sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries are characterized by low production costs and high safety performance. Furthermore, sodium resources are abundant and widely distributed, making them promising for applications in portable electronic devices, electrochemical energy storage, and electric vehicles. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries; both utilize the transfer of ions between the positive and negative electrodes to store and release electrical energy. The positive and negative electrode materials are crucial to the development of sodium-ion batteries, largely determining their energy density and cost. Currently, my country has made significant progress in the research of sodium-ion battery positive electrodes, achieving good results using layered oxides, polyanionic compounds, and Prussian blue analogues as positive electrode materials. However, the radius of sodium ions (0.102 nm) is much larger than that of lithium ions (0.076 nm), meaning that graphite anode materials suitable for lithium-ion batteries are not suitable for sodium-ion batteries. Currently, sodium-ion battery anode materials mainly include carbon-based, organic, alloy, conversion-type, and metal oxide materials. Among carbon-based anode materials, hard carbon is the most promising due to its advantages such as high reversible capacity, structural stability, and low sodium storage potential. However, the reported initial coulombic efficiency of hard carbon rarely exceeds 85%, far lower than that of graphite in lithium-ion batteries. A lower initial coulombic efficiency means a higher irreversible capacity during the first charge-discharge cycle, leading to rapid capacity decay and low energy density in sodium-ion batteries. Although various strategies have been adopted domestically and internationally to improve the electrochemical performance of hard carbon, the overall electrochemical performance of currently prepared hard carbon anode materials, including initial coulombic efficiency and specific capacity, remains low. Furthermore, the complex preparation process limits the practical application of hard carbon.

[0003] The information disclosed in the background section is only for enhancing the understanding of the background of this invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] This invention provides a method for preparing hard carbon anode material for sodium-ion batteries, which improves the electrochemical performance of hard carbon and enhances its initial coulombic efficiency and specific capacity.

[0005] A method for preparing a hard carbon anode material for sodium-ion batteries includes: The first step is to prepare a graphene oxide-containing phenolic sol, in which phenols and aldehydes are used as raw materials and alcohols are used as solvents. A small amount of graphene oxide suspension is added to the alcohol solvent and mixed evenly by ultrasonic vibration. Then, aldehydes, phenols and hexamethylenetetramine are added in sequence and stirred evenly to prepare a graphene oxide-containing phenolic sol. The second step is to solidify the graphene oxide-containing phenolic gel, wherein the graphene oxide-containing phenolic sol is placed in a water bath to solidify, so that the graphene oxide-containing phenolic sol becomes the graphene oxide-containing phenolic gel. The third step involves preparing a blocky hard carbon precursor based on graphene oxide-containing phenolic gel. Specifically, the graphene oxide-containing phenolic gel is heated to 700-1000℃ under a protective atmosphere using a heating device for the first carbonization. After holding at the temperature, it is naturally cooled to obtain the blocky hard carbon precursor. The fourth step is grinding and pulverizing, in which the blocky hard carbon precursor is ground and pulverized into powdered hard carbon precursor. The fifth step is higher temperature carbonization, in which the powdered hard carbon precursor is placed in a heating device and heated to 1100~1500℃ in a protective atmosphere for a second carbonization. After holding at the temperature, it is naturally cooled, and argon or nitrogen is introduced throughout the process to obtain hard carbon anode material.

[0006] Preferably, in the first step, the molar ratio of aldehydes to phenols is 2:1, the molar ratio of hexamethylenetetramine to phenols is 0.01:1, the molar ratio of alcohols to phenols ranges from 1 to 6:1, and the mass ratio of graphene oxide suspension to phenols ranges from 0.01 to 0.1:1, wherein the mass of resorcinol remains constant.

[0007] Preferably, in the second step, the graphene oxide-containing phenolic sol is placed in a water bath at 50°C and cured for 24 to 48 hours to transform the graphene oxide-containing phenolic sol into a graphene oxide-containing phenolic gel. Preferably, in the third step, the graphene oxide-containing phenolic gel is placed in a tube furnace, a vacuum is first drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is increased to 700-1000℃ at a rate of 2.0-5.0℃ / min, and held at this temperature for 2-5 hours. Then it is naturally cooled, and argon or nitrogen is introduced at a flow rate of 20-100mL / min throughout the process to obtain a blocky hard carbon precursor.

[0008] Preferably, in the fourth step, the blocky hard carbon precursor is placed in a mortar and ground into powder.

[0009] Preferably, in the fifth step, the powdered hard carbon precursor is placed in a tube furnace, a vacuum is first drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is then increased to 1100-1500℃ at a heating rate of 2.0-5.0℃ / min for high-temperature carbonization. The temperature is held at this temperature for 2-5 hours, and then the material is allowed to cool naturally. Argon or nitrogen is introduced throughout the process at a flow rate of 20-100mL / min to obtain the hard carbon anode material.

[0010] In the method for preparing a hard carbon anode material for sodium-ion batteries, the mass concentration of the graphene oxide suspension is 1 wt.%.

[0011] In the preparation method of the sodium-ion battery hard carbon anode material, the fifth step involves a carbonization temperature of 1500℃ to improve the initial coulombic efficiency and specific capacity.

[0012] In the method for preparing a hard carbon anode material for sodium-ion batteries, the molar ratio of ethanol to resorcinol is 3:1 to improve the electrochemical performance of the hard carbon anode material.

[0013] In the method for preparing a hard carbon anode material for sodium-ion batteries, the mass ratio of the graphene oxide suspension to resorcinol is 0.075:1, which enables the initial coulombic efficiency of the hard carbon anode material to reach 87.6% and the specific capacity to be 359.8 mAh / g.

[0014] In the preparation method of a sodium-ion battery hard carbon anode material, in the second step, the graphene oxide-containing phenolic sol is placed in a water bath at 50°C and cured for 36 hours to transform the graphene oxide-containing phenolic sol into a graphene oxide-containing phenolic gel.

[0015] In the fifth step of the method for preparing a hard carbon anode material for sodium-ion batteries, a vacuum is first drawn, and then argon or nitrogen is introduced into the tube furnace to replace the air in the tube furnace twice. Then, the temperature is raised to 1500 ℃ at a heating rate of 2.0 ℃ / min, held at this temperature for 2 hours, and then cooled naturally. Argon or nitrogen is introduced at a flow rate of 50 mL / min throughout the process to obtain the hard carbon anode material.

[0016] A hard carbon anode, prepared by the method described above.

[0017] The hard carbon anode has an initial coulombic efficiency of ≥85% and a reversible specific capacity of ≥350 mAh / g.

[0018] A sodium-ion battery comprising the hard carbon negative electrode.

[0019] Compared with existing technologies, this invention has the following advantages: This invention uses a combination of graphene oxide and alcohol solvents to synthesize a hard carbon precursor, followed by high-temperature carbonization to prepare a hard carbon anode material. This hard carbon anode material exhibits excellent electrochemical performance. The preparation process of this invention is simple, easy to operate, has a short cycle time, and low cost. During the synthesis of the hard carbon precursor, a small amount of graphene oxide suspension (1 wt.%) is used, followed by simple processes such as curing, pre-carbonization, grinding, and high-temperature carbonization to prepare a hard carbon anode material with smaller interlayer spacing, fewer defects, and a smaller specific surface area. Attached Figure Description

[0020] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0021] In the attached diagram: Figure 1 This is a process flow diagram of a method for preparing hard carbon anode material in one embodiment of the present invention; Figure 2 This is an XRD pattern of a hard carbon anode material in one embodiment of the present invention; Figure 3 This is an XRD pattern (a:HC, b:GOHC) of a hard carbon anode material in one embodiment of the present invention. Figure 4 This is a Raman spectrum of a hard carbon anode material in one embodiment of the present invention; Figure 5 This is a Raman peak spectrum of a hard carbon anode material in one embodiment of the present invention (a: HC, b: GOHC). Figure 6 This is a TEM image (a:HC, b:GOHC) of a hard carbon anode material in one embodiment of the present invention. Figure 7 This is the first-cycle constant current charge-discharge curve of the hard carbon anode material prepared according to an embodiment of the present invention.

[0022] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0023] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0024] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0025] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0026] like Figures 1 to 7 As shown, the preparation method of hard carbon anode material for sodium-ion batteries includes the following steps: The first step is to prepare a graphene oxide-containing phenolic sol. Phenolic and aldehyde substances are used as raw materials, and alcohols are used as solvents. Graphene oxide suspension is added to the alcohol solvent and mixed uniformly by ultrasonic vibration. Then, aldehydes, phenols, and hexamethylenetetramine are added sequentially, and the mixture is stirred uniformly with a magnetic stirrer. The molar ratio of aldehydes to phenols is 2:1, the molar ratio of hexamethylenetetramine to phenols is 0.01:1, the molar ratio of alcohols to phenols ranges from 1 to 6:1, and the mass ratio of graphene oxide suspension to phenols ranges from 0.01 to 0.1:1. The mass of resorcinol is kept constant. The mixture is then stirred to prepare the graphene oxide-containing phenolic sol. The second step is to solidify the graphene oxide-containing phenolic gel. Specifically, the graphene oxide-containing phenolic sol is placed in a water bath at 50°C and solidified for 24 to 48 hours to transform the graphene oxide-containing phenolic sol into a graphene oxide-containing phenolic gel. The third step involves preparing a bulk hard carbon precursor based on graphene oxide-containing phenolic gel. The graphene oxide-containing phenolic gel is placed in a tube furnace, a vacuum is first drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is increased to 700-1000℃ at a rate of 2.0-5.0℃ / min, and held at this temperature for 2-5 hours. Then it is allowed to cool naturally. Argon or nitrogen is introduced at a flow rate of 20-100mL / min throughout the process to obtain the bulk hard carbon precursor. The fourth step is grinding and pulverizing, in which the blocky hard carbon precursor is placed in a mortar and ground and pulverized into a powdered hard carbon precursor. The fifth step is high-temperature carbonization. In this step, the powdered hard carbon precursor is placed in a tube furnace. First, a vacuum is drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is then increased to 1100-1500℃ at a rate of 2.0-5.0℃ / min for high-temperature carbonization. This temperature is maintained for 2-5 hours, and then the material is allowed to cool naturally. Argon or nitrogen is introduced at a flow rate of 20-100mL / min throughout the process to obtain the hard carbon anode material.

[0027] In the above embodiments, the hard carbon anode material prepared according to the method exhibits a first-stage coulombic efficiency as high as 87.6% and a specific capacity of 359.8 mAh g⁻¹. -1 For example, phenolic resin gel synthesized from resorcinol and furfural as raw materials combined with ethanol solvent is used as a hard carbon precursor. The main time-consuming steps are: the second step of curing the graphene oxide-containing phenolic sol, which takes 1-2 days; the third step of pre-carbonization, which takes 1 day; and the fifth step of high-temperature carbonization, which takes 1 day. The entire preparation process is simple, with a total time of about 3-4 days and a short preparation cycle. The hard carbon anode material prepared by this invention has a smaller interlayer spacing, fewer defects, and a smaller specific surface area. Ethanol solvent has a low boiling point and easily volatilizes from the phenolic resin gel when heated, forming pre-fabricated open channels in the phenolic resin gel matrix. This allows small gas molecules such as CO2 and CO generated during the carbonization process to escape directionally from the pre-fabricated open channels, effectively improving the pore structure of hard carbon. The hydrogen bonds between graphene oxide and phenolic resin can interact. During pyrolysis, the aromatic rings near graphene have a strong tendency to grow graphite-like microcrystals along the graphene layers. 3 to sp 2 The significant transformation of hybrid carbon endows hard carbon with fewer defects and a smaller specific surface area. The hard carbon anode material prepared using this invention exhibits high initial coulombic efficiency and large specific capacity. The synthesis of the hard carbon precursor using a combination of graphene oxide and ethanol solvent offers the advantage of easily tunable structure. During carbonization, the pore-forming effect of the ethanol solvent and the in-situ graphitization-induced effect of graphene oxide can be synergistically utilized. By employing pre-carbonization and grinding processes followed by high-temperature carbonization, the microstructure and graphitization degree of the hard carbon anode material are effectively improved, thereby enhancing its electrochemical performance.

[0028] In a preferred embodiment of the method for preparing a hard carbon anode material for a sodium-ion battery, the mass concentration of the graphene oxide suspension is 1 wt.%.

[0029] In a preferred embodiment of the method for preparing a hard carbon anode material for a sodium-ion battery, the fifth step involves a carbonization temperature of 1500°C to improve the initial coulombic efficiency and specific capacity.

[0030] In a preferred embodiment of the method for preparing a hard carbon anode material for a sodium-ion battery, the molar ratio of ethanol to resorcinol is 3:1 to improve the electrochemical performance of the hard carbon anode material.

[0031] In a preferred embodiment of the method for preparing a hard carbon anode material for a sodium-ion battery, the mass ratio of the graphene oxide suspension to resorcinol is 0.075:1, which results in the initial coulombic efficiency of the hard carbon anode material reaching 87.6% and the specific capacity being 359.8 mAh / g.

[0032] In a preferred embodiment of the method for preparing a hard carbon anode material for a sodium-ion battery, in the second step, the graphene oxide-containing phenolic sol is placed in a water bath at 50°C and cured for 36 hours to transform the graphene oxide-containing phenolic sol into a graphene oxide-containing phenolic gel.

[0033] In a preferred embodiment of the method for preparing a hard carbon anode material for sodium-ion batteries, in the fifth step, a vacuum is first drawn, and then argon or nitrogen is introduced into the tube furnace to replace the air in the tube furnace twice. Then, the temperature is raised to 1500 ℃ at a heating rate of 2.0 ℃ / min, held at this temperature for 2 hours, and then cooled naturally. Argon or nitrogen is introduced at a flow rate of 50 mL / min throughout the process to obtain the hard carbon anode material.

[0034] A hard carbon anode, prepared by the method described above.

[0035] In a preferred embodiment of the hard carbon anode, its initial coulombic efficiency is ≥85% and its reversible specific capacity is ≥350 mAh / g.

[0036] A sodium-ion battery comprising the hard carbon negative electrode.

[0037] In one embodiment, the phenolic substance refers to any one of resorcinol (C6H6OH) and hydroquinone (C6H6OH); The aldehydes mentioned refer to any one of furfural (C5H4O2) and formaldehyde (HCHO); The alcohols refer to any one of methanol (CH3OH) and ethanol (C2H5OH).

[0038] In one embodiment, a phenolic resin gel synthesized from resorcinol and furfural as raw materials and combined with ethanol solvent is used as a hard carbon precursor. A small amount of graphene oxide suspension (1 wt.%) is added during the synthesis of the hard carbon precursor. Then, a hard carbon anode material with smaller interlayer spacing, fewer defects, and smaller specific surface area is prepared through simple curing and high-temperature carbonization processes. Since graphene oxide is soluble in ethanol solvent, adding a small amount of graphene oxide during the sol-gel synthesis of phenolic resin gel is beneficial for the uniform dispersion of graphene oxide and its embedding on the nanoframework of the prepared hard carbon. This allows the ethanol solvent to synergistically create pores and the graphene oxide to induce in-situ graphitization of the hard carbon during the carbonization process. Simultaneously, the pre-carbonization and grinding processes, followed by high-temperature carbonization, effectively improve the microstructure and graphitization degree of the hard carbon anode material, solving the key problems of low initial coulombic efficiency and specific capacity that limit the practical application of hard carbon. This completes the key technology development for improving the electrochemical performance of hard carbon anode materials and has industrialization prospects. The preparation method of the hard carbon anode material provided by this invention includes the following steps: Step 1: Preparation of phenolic sol containing graphene oxide: A small amount of graphene oxide suspension (1 wt.%) was added to an ethanol solvent and mixed evenly by ultrasonic vibration. Then, furfural, resorcinol, and hexamethylenetetramine were added sequentially. The molar ratio of furfural to resorcinol was 2:1, the molar ratio of hexamethylenetetramine to resorcinol was 0.01:1, the molar ratio of ethanol to resorcinol ranged from 1 to 6:1, and the mass ratio of graphene oxide suspension to resorcinol ranged from 0.01 to 0.1:1. The mass of resorcinol was kept constant. The mixture was then stirred evenly with a magnetic stirrer to prepare a graphene oxide phenolic sol.

[0039] The second step is to solidify the graphene oxide-containing phenolic gel. The graphene oxide-containing phenolic sol is placed in a water bath at 50°C and solidified for 24 to 48 hours to transform the graphene oxide-containing phenolic sol into a graphene oxide-containing phenolic gel. The third step involves preparing a bulk hard carbon precursor based on graphene oxide-containing phenolic gel. The graphene oxide-containing phenolic gel is placed in a tube furnace, a vacuum is first drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is increased to 700-1000℃ at a rate of 2.0-5.0℃ / min, and held at this temperature for 2-5 hours. Then it is allowed to cool naturally, with argon or nitrogen being introduced at a flow rate of 20-100mL / min throughout the process to obtain the bulk hard carbon precursor.

[0040] The fourth step is grinding and pulverizing. Place the blocky hard carbon precursor in a mortar and grind it into powder.

[0041] The fifth step is high-temperature carbonization. The powdered hard carbon precursor is placed in a tube furnace. First, a vacuum is drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is then increased to 1100-1500℃ at a rate of 2.0-5.0℃ / min for high-temperature carbonization. This temperature is maintained for 2-5 hours, and then the material is allowed to cool naturally. Argon or nitrogen is introduced at a flow rate of 20-100mL / min throughout the process to obtain the hard carbon anode material.

[0042] Example 1: The first step is to prepare a graphene oxide-containing phenolic sol: a small amount of graphene oxide suspension (1 wt.%) is added to the ethanol solvent and mixed evenly by ultrasonic vibration. Then, furfural, resorcinol, and hexamethylenetetramine are added sequentially. The furfural, hexamethylenetetramine, and ethanol are weighed according to a certain molar ratio with resorcinol. The molar ratio of furfural to resorcinol is 2:1, the molar ratio of hexamethylenetetramine to resorcinol is 0.01:1, the molar ratio of ethanol to resorcinol is in the range of 3:1, and the mass ratio of graphene oxide suspension to resorcinol is 0.075:1, of which the mass of resorcinol is 5.0 g. Then, the mixture is stirred evenly with a magnetic stirrer to prepare the graphene oxide-containing phenolic sol.

[0043] The second step is the curing of the graphene oxide-containing phenolic gel: The graphene oxide-containing phenolic sol was placed in a normal pressure environment at 50°C for 36 hours to cure, thus transforming the graphene oxide-containing phenolic sol into a graphene oxide-containing phenolic gel.

[0044] The third step involves preparing a bulk hard carbon precursor based on graphene oxide-containing phenolic gel. The graphene oxide-containing phenolic gel is placed in a tube furnace, a vacuum is first drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is increased to 1000℃ at a rate of 5.0℃ / min, and held at this temperature for 2 hours. Then it is allowed to cool naturally, with argon or nitrogen being introduced at a flow rate of 50mL / min throughout the process to obtain the bulk hard carbon precursor.

[0045] The fourth step is grinding and pulverizing. Place the blocky hard carbon precursor in a mortar and grind it into powder.

[0046] The fifth step is high-temperature carbonization. The powdered hard carbon precursor is placed in a tube furnace. First, a vacuum is drawn, and then argon or nitrogen is introduced into the tube furnace. The temperature is then increased to 1500℃ at a rate of 5.0℃ / min for high-temperature carbonization. This temperature is maintained for 2 hours, and then the material is allowed to cool naturally. Argon or nitrogen is introduced at a flow rate of 50mL / min throughout the process to obtain the hard carbon anode material.

[0047] In this invention, hard carbon prepared by adding a small amount of graphene oxide during the hard carbon precursor synthesis process is denoted as GOHC, and hard carbon prepared without adding graphene oxide is denoted as HC. Figure 2The XRD patterns of two hard carbons, HC and GOHC, are shown. Two broad peaks appear at diffraction angles of approximately 23° and 43° at 2θ, corresponding to the (002) peak and (100) peak in the hard carbon structure, respectively, indicating that these two hard carbons are amorphous carbons with a low degree of graphitization. Based on the peak position changes of the (002) peaks of the two hard carbons, it can be seen that the (002) peak position of GOHC hard carbon shifts to a higher angle. To accurately determine the interlayer spacing of hard carbons, the XRD patterns of the two hard carbons are refined, and the (002) peak position of HC hard carbon is found to be at 2θ = 23.436°. o The (002) peak of GOHC hard carbon is located at 2θ = 23.843. o ,like Figure 3 As shown in (a, b), the interlayer spacing (d002) of the hard carbon anode material was calculated using the Bragg equation (2d002sinθ=nλ). The interlayer spacing of GOHC hard carbon (0.373 nm) is smaller than that of HC hard carbon (0.382 nm), indicating that the addition of graphene oxide reduces the hard carbon interlayer spacing. Figure 6 TEM comparison images of hard carbon anode materials show that the interlayer spacing of the ordered regions in HC is 0.38 nm, while that in GOHC is 0.7 nm. This indicates that the interlayer spacing of hard carbon prepared by adding graphene oxide is smaller. The integral ratio of the peak area, I, was calculated. D1 / I G It can assess the degree of disorder in hard carbon materials and calculate the Ig of HC and GOHC hard carbons. D1 / I G The ratios are 1.26 and 1.16 respectively, such as Figure 4 and 5 As shown, this indicates that the hard carbon anode material prepared with the addition of graphene oxide has a lower degree of disorder and a higher degree of graphitization, and that graphene oxide has the effect of inducing the graphitization of the hard carbon anode material. The structural parameters of the hard carbon anode materials prepared with and without the addition of graphene oxide are shown in Table 1.

[0048] Table 1 Structural parameters of hard carbon anode materials The hard carbon anode material prepared by this invention has an initial coulombic efficiency of 87.6% and a specific capacity of 359.8 mAh g⁻¹. -1 .like Figure 7 The first-cycle constant current charge-discharge curve of the hard carbon anode material in Example 1 is shown.

[0049] Examples 2-27 The process parameters used in Examples 2-27 are shown in Table 2. The process parameters that affect the electrochemical performance of the hard carbon anode material are mainly the raw material ratio for preparing the graphene oxide phenolic sol and the high-temperature carbonization temperature. The molar ratio of furfural to resorcinol is 2:1, and the molar ratio of hexamethylenetetramine to resorcinol is 0.01:1, which remains unchanged. Therefore, Examples 2-27 mainly change the three parameters of ethanol, graphene oxide and high-temperature carbonization temperature to further explain the present invention. Except for the process parameters listed, the other unlisted process parameters are the same as those in Example 1. In the second step of the graphene oxide-containing phenolic gel curing process, the curing time has no significant impact on the product performance, provided that curing is ensured. In the third and fifth steps of the carbonization process, argon or nitrogen is introduced into the tube furnace to keep the graphene oxide-containing phenolic gel in an inert atmosphere and prevent it from being oxidized at high temperatures. As long as the oxygen-free environment in the tube furnace is ensured, the number of times argon or nitrogen is introduced, the number of times air is replaced, and the flow rate of argon or nitrogen introduced have no significant impact on the electrochemical performance of the hard carbon anode material.

[0050] Table 2. Preparation process parameters and electrochemical performance of hard carbon anode materials Furthermore, this invention uses resorcinol and furfural as raw materials combined with ethanol solvent to synthesize phenolic resin gel, providing a structurally stable hard carbon precursor with high carbon yield and good controllability and pyrolysis performance. A graphene oxide suspension (1 wt.%) is introduced and uniformly dispersed in the hard carbon precursor during the phenolic resin gelation process. During subsequent high-temperature carbonization, it induces in-situ growth of hard carbon-like graphite microcrystals, improving the structural order of hard carbon and reducing defects. Ethanol solvent has a low boiling point and easily volatilizes from the phenolic resin gel upon heating, forming pre-fabricated open channels in the phenolic resin gel matrix. This allows small gas molecules such as CO2 and CO generated during the carbonization process to escape directionally from these pre-fabricated open channels, effectively improving the pore structure of hard carbon. Ethanol, as a solvent, has a low boiling point and is easily volatile; forming pre-fabricated channels in the phenolic resin gel matrix allows for the directional escape of decomposed gases, optimizing the pore structure. Controlling the mass ratio of graphene oxide to resorcinol (0.01–0.1:1) ensures uniform distribution of graphene oxide in the precursor, preserving the phenolic resin network structure while effectively leveraging the in-situ graphitization-inducing effect of graphene oxide. Controlling the molar ratio of ethanol to resorcinol (1–6:1) regulates the degree of gel crosslinking and pore structure, influencing the final microstructure and electrochemical properties of the hard carbon material. A normal pressure curing process (curing at 50°C for 24–48 hours) achieves the sol-gel transformation, forming a three-dimensional network structure that provides a stable framework for subsequent carbonization. High-temperature carbonization (1100–1500°C, heating rate 2–5°C / min) promotes the pyrolysis of phenolic resin into hard carbon material and synergistically induces the graphitization of the carbon structure. Carbonization under an argon or nitrogen protective atmosphere (flow rate 50–200 mL / min) prevents oxidation of the material at high temperatures, maintains the integrity of the carbon structure, and ensures stable product performance. Multiple air replacements (2-3 times) within the furnace ensure an oxygen-free environment during carbonization, preventing material oxidation or side reactions. A five-step method (sol-gel → curing → pre-carbonization → grinding → carbonization) is employed to prepare hard carbon materials. This method is simple, has a short cycle time, and is suitable for industrial application. Compared to traditional solvothermal methods, it is easier to operate and control. The initial coulombic efficiency is significantly improved: through the synergistic effect of graphene oxide and ethanol solvent, and high-temperature carbonization, the initial coulombic efficiency reaches 87.6%. Specific capacity is greatly improved: reaching 359.8 mAh / g. It exhibits strong structural control capabilities, smaller interlayer spacing, lower defect density, smaller specific surface area, and is more conducive to sodium ion insertion / extraction.The parameter adjustment experiments of the system in Examples 1-27 showed that the graphene oxide content has a significant impact on the initial coulombic efficiency and specific capacity, and the optimal molar ratio of graphene oxide to resorcinol is 0.075:1. The amount of ethanol affects the gel structure and pore distribution, and the optimal molar ratio of ethanol to resorcinol is 3:1. The carbonization temperature of 1500℃ yields the best overall performance, with an initial coulombic efficiency of 87.6% and a specific capacity of 359.8 mAh / g. The obtained hard carbon material has excellent cycle stability and rate performance, and is suitable for high-performance sodium-ion battery anodes.

[0051] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: The first step is to prepare a graphene oxide-containing phenolic sol, in which phenols and aldehydes are used as raw materials and alcohols are used as solvents. A small amount of graphene oxide suspension is added to the alcohol solvent and mixed evenly by ultrasonic vibration. Then, aldehydes, phenols and hexamethylenetetramine are added in sequence and stirred evenly to prepare a graphene oxide-containing phenolic sol. The second step is to solidify the graphene oxide-containing phenolic gel, wherein the graphene oxide-containing phenolic sol is placed in a water bath to solidify, so that the graphene oxide-containing phenolic sol becomes the graphene oxide-containing phenolic gel. The third step involves preparing a blocky hard carbon precursor based on graphene oxide-containing phenolic gel. Specifically, the graphene oxide-containing phenolic gel is heated to 700-1000℃ under a protective atmosphere using a heating device for the first carbonization. After holding at the temperature, it is naturally cooled to obtain the blocky hard carbon precursor. The fourth step is grinding and pulverizing, in which the blocky hard carbon precursor is ground and pulverized into powdered hard carbon precursor. The fifth step is higher temperature carbonization, in which the powdered hard carbon precursor is placed in a heating device and heated to 1100~1500℃ in a protective atmosphere for a second carbonization. After holding at the temperature, it is naturally cooled, and argon or nitrogen is introduced throughout the process to obtain hard carbon anode material.

2. The method for preparing a hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that, Preferably, the mass concentration of the graphene oxide suspension is 1 wt.%.

3. The method for preparing a hard carbon anode material for a sodium-ion battery according to claim 1, characterized in that, The fifth step involves a carbonization temperature of 1500°C to improve the initial coulombic efficiency and specific capacity.

4. The method for preparing a hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that, The molar ratio of ethanol to resorcinol is 3:1 to improve the electrochemical performance of the hard carbon anode material.

5. The method for preparing a hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that, The mass ratio of the graphene oxide suspension to resorcinol is 0.075:1, which enables the hard carbon anode material to achieve an initial coulombic efficiency of 87.6% and a specific capacity of 359.8 mAh / g.

6. The method for preparing a hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that, In the second step, the graphene oxide-containing phenolic sol is placed in a water bath at 50°C and cured for 36 hours, so that the graphene oxide-containing phenolic sol becomes a graphene oxide-containing phenolic gel.

7. The method for preparing a hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that, The fifth step involves first evacuating the furnace and then filling it with argon or nitrogen to replace the air in the furnace twice. The temperature is then increased to 1500 ℃ at a rate of 2.0 ℃ / min and held at this temperature for 2 hours. The furnace is then allowed to cool naturally, with argon or nitrogen being introduced at a flow rate of 50 mL / min throughout the process to obtain the hard carbon anode material.

8. A hard carbon anode, characterized in that, It is prepared by the method according to any one of claims 1-7.

9. The hard carbon anode according to claim 8, characterized in that, Its initial coulombic efficiency is ≥85%, and its reversible specific capacity is ≥350 mAh / g.

10. A sodium-ion battery, characterized in that, It includes the hard carbon anode according to claim 8 or 9.

Images