Preparation method of sodium ion battery modified anthracite-based hard carbon electrode material

Abstract

A method for preparing anthracite-based hard carbon electrode material modified for sodium-ion batteries is disclosed. This method addresses the technical problems of existing anthracite-based hard carbon electrode material modification methods, which are complex, require stringent equipment, have high production costs, and struggle to achieve deep molecular-level structural modification. The proposed method involves uniformly mixing anthracite powder with a modifier to prepare a primary carbon source. Then, under inert gas protection, the mixture is heated to 300–500 °C and held for 1–3 h, followed by heating to 1000–1400 °C and holding for another 1–3 h to obtain the sodium-ion battery modified anthracite-based hard carbon electrode material. The material exhibits an initial capacity of 250–252 mAh / g and a capacity retention of 81%–83% after 1000 cycles at a current density of 1 A / g, making it suitable for use in sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to a method for preparing anthracite-based hard carbon electrode materials. Background Technology

[0002] In recent years, although lithium-ion batteries have dominated the market, their further application in large-scale energy storage has been severely hampered by the scarcity, uneven distribution, and continuous price fluctuations of lithium resources. In contrast, sodium-ion batteries, due to their abundant sodium resources, low cost, excellent low-temperature performance, and similar working mechanism to lithium-ion batteries, are considered a highly promising next-generation large-scale energy storage technology. In the research and development of sodium-ion batteries, finding inexpensive and high-performance anode materials is crucial for their commercialization. Carbon-based materials, especially hard carbon, have become the preferred anode material for sodium batteries due to their high sodium storage capacity, low operating potential, and good structural stability. However, the performance of hard carbon largely depends on the type of precursor. Currently, commonly used hard carbon precursors are mostly biomass (such as sugars and shells) or synthetic resins (such as phenolic resins). Although they have excellent performance, they generally suffer from high raw material costs, low carbon yield, or seasonal and geographical limitations in sourcing, making it difficult to meet the needs of large-scale production.

[0003] Coal, as an abundant, inexpensive, and high-carbon mineral resource, is an ideal precursor for the preparation of hard carbon materials. Among them, anthracite has attracted much attention due to its high degree of metamorphism, stable natural carbon skeleton structure, and high carbon yield. However, there are significant limitations to using natural anthracite directly as a negative electrode material for sodium batteries. First, the microcrystalline structure is too dense: the interlayer spacing of anthracite after direct carbonization is usually small, making it difficult to allow for the rapid insertion and extraction of larger sodium ions, resulting in poor kinetic performance. Second, structural defects are uncontrollable: during the pyrolysis process of anthracite, the decomposition of internal oxygen-containing functional groups and the violent volatilization of small-molecule organic matter leave a large number of open defects and unstable active sites in the carbon skeleton. These defects can cause excessive decomposition of the electrolyte and capture irreversible sodium ions during the first charge and discharge, forming an excessively thick solid electrolyte interface film, resulting in extremely low initial coulombic efficiency and poor cycle stability.

[0004] To overcome the aforementioned defects of anthracite, current research primarily employs techniques such as chemical vapor deposition (CVD) or atomic layer deposition (ALD) to repair the surface of coal-based carbon materials. While these methods effectively reduce defect concentration and improve ICE (Induced Electron Efficiency), they are complex processes, require stringent equipment, are costly to produce, and struggle to achieve deep molecular-level structural modification. Therefore, developing coal-based hard carbon anode materials with high initial coulombic efficiency, high capacity, and long lifetime by utilizing low-cost modifiers and employing simple and efficient processes to regulate the microstructure of anthracite precursors, thereby achieving "in-situ defect capture and repair" while expanding sodium storage space, has become a crucial issue urgently needing to be addressed in the field of sodium-ion batteries. Summary of the Invention

[0005] The present invention aims to solve the technical problems of existing methods for modifying anthracite-based hard carbon electrode materials, which are complex, require stringent equipment, have high production costs, and are difficult to achieve deep molecular-level structural modification. Instead, it provides a method for preparing anthracite-based hard carbon electrode materials modified for sodium-ion batteries.

[0006] The preparation method of the sodium-ion battery modified anthracite-based hard carbon electrode material of the present invention is carried out according to the following steps:

[0007] 1. Mix the purified anthracite powder with the modifier evenly to obtain the original carbon source. This step utilizes the abundant oxygen-containing functional groups (hydroxyl, carboxyl, etc.) in the modifier to pre-contact with the active sites on the surface of the anthracite, providing a reaction basis for subsequent molecular-level grafting.

[0008] 2. The original carbon source is placed in a furnace and heated to 300–500 °C at a heating rate of 1–10 °C / min under inert gas protection, and held for 1–3 h to obtain a modified anthracite precursor; then, under a protective atmosphere, the temperature is raised to 1000–1400 °C and held for 1–3 h, followed by natural cooling to room temperature to obtain a modified anthracite-based hard carbon electrode material for sodium-ion batteries; in this step, the temperature is raised to 300–500 °C / min. During the low-temperature heat treatment stage at ℃, the modifier molecules undergo chemical reactions such as dehydration condensation with the oxygen-containing groups on the surface of anthracite. This in-situ modification strategy can block the active defects in the structure of anthracite, reduce the violent escape of gas in the subsequent high-temperature stage, and inhibit the generation of physical defects from the source, thereby significantly improving the initial coulombic efficiency of the material. After grafting and repair, the anthracite is transformed into a highly disordered hard carbon structure at high temperature. The grafted organic molecules play a structural support role in the carbonization process, expanding the carbon interlayer spacing and providing a wider transport channel for the rapid insertion / extraction of sodium ions.

[0009] Furthermore, the modified material described in step one is glucose, sucrose, cellulose, or lignin.

[0010] Furthermore, the mass ratio of anthracite to modifier mentioned in step one is (1~19):1.

[0011] Furthermore, the mixing method of anthracite and modifier in step one is ball milling, manual grinding, tableting, or solution impregnation.

[0012] Furthermore, the ball milling process involves placing anthracite powder and a modifier in the ball mill jar of a planetary ball mill, adding zirconia balls as the grinding medium, and controlling the ball-to-material mass ratio at 10:1. Subsequently, the mixture is ball-milled at 300 rpm for 6 hours, with a 10-minute pause every 30 minutes to prevent the sample from overheating.

[0013] Furthermore, the manual grinding and mixing process involves placing the anthracite powder and the modifier in an agate mortar and grinding them continuously for 40-60 minutes using a pestle to ensure that the two components are fully and evenly mixed.

[0014] Furthermore, the tableting method involves grinding anthracite powder and modifier in an agate mortar for 20-30 minutes to achieve initial uniform mixing; then transferring the mixed powder to a mold, applying a pressure of 20-22 MPa on a tablet press for 2 minutes, demolding, and removing the raw carbon source in the form of discs.

[0015] Furthermore, the solution impregnation method is as follows: anthracite powder is added to deionized water and ultrasonically dispersed for 30 minutes to obtain a uniform suspension; then the modifier is added to the anthracite suspension, magnetically stirred at room temperature for 5-6 hours, and then transferred to a vacuum drying oven at 75-80 ℃ for 10-12 hours to obtain a uniformly impregnated composite original carbon source.

[0016] Furthermore, the inert gas mentioned in step two is argon, nitrogen, or carbon dioxide.

[0017] During the carbonization process, anthracite exhibits numerous defects and residual oxygen-containing groups on its surface due to volatile matter release and structural reorganization. This leads to the formation of an excessively thick SEI film during the initial charge-discharge cycle, resulting in irreversible sodium ion trapping and a low initial coulombic efficiency (ICE) of the battery. Furthermore, the small interlayer spacing of the hard carbon derived from pure anthracite hinders the rapid insertion and diffusion of sodium ions, limiting the material's sodium storage capacity. This invention utilizes a simple, single-step pre-carbonization "molecular grafting" technique to fill active defect sites in the anthracite structure, repairing surface defects in situ. This helps reduce irreversible side reactions of the electrolyte on the surface and simultaneously expands the interlayer spacing, thereby significantly improving ICE, specific capacity, and cycle stability while maintaining low cost.

[0018] The sodium-ion battery modified anthracite-based hard carbon electrode material prepared by this invention has an initial capacity of 250~252 mAh / g and a capacity retention rate of 81%~83% after 1000 cycles at a current density of 1 A / g, and can be used in the field of sodium-ion batteries. Attached Figure Description

[0019] Figure 1 XRD patterns of the original anthracite carbon material and the hard carbon products obtained by adding glucose, sucrose, cellulose and lignin in Examples 1-4;

[0020] Figure 2 Raman spectra of the modified anthracite-based hard carbon electrode materials for sodium-ion batteries obtained by adding glucose, sucrose, cellulose, and lignin to Examples 1-4.

[0021] Figure 3 The infrared spectra of the original glucose, the original anthracite, and the glucose-modified anthracite precursor during the low-temperature heat treatment stage in Example 1 are shown.

[0022] Figure 4 XPS images of anthracite-based hard carbon and glucose-modified anthracite-based hard carbon in Example 1;

[0023] Figure 5 The XRD patterns of the samples prepared in Examples 1 and 5-6, as well as glucose and anthracite;

[0024] Figure 6 Raman spectra of the samples prepared in Examples 1 and 5-6;

[0025] Figure 7 Scanning electron microscope (SEM) images of the sodium-ion battery modified anthracite-based hard carbon electrode materials prepared in Examples 7-9 and 1. Detailed Implementation

[0026] The beneficial effects of the present invention will be verified using the following examples.

[0027] Example 1: The preparation method of the sodium-ion battery modified anthracite-based hard carbon electrode material in this example is carried out according to the following steps:

[0028] First, the anthracite powder that has undergone impurity removal treatment is ground thoroughly in an agate mortar with the modifier glucose (GA) at a mass ratio of 90:10 for 30 min to ensure that the two components are initially and uniformly mixed. Then, the mixed powder is transferred to a mold, and after applying a pressure of 20 MPa on a tablet press for 2 min, it is demolded to obtain a round plate-shaped original carbon source. This step utilizes the abundant oxygen-containing functional groups (hydroxyl, carboxyl, etc.) in glucose to pre-contact with the active sites on the surface of anthracite, providing a reaction basis for subsequent molecular-level grafting.

[0029] 2. The original carbon source was placed in a tube furnace and heated to 400℃ for 2 h at a heating rate of 5 ℃ / min under argon protection to obtain a modified anthracite precursor. Then, under a protective atmosphere, it was heated to 1200℃ at a heating rate of 5 ℃ / min and held for 2 h, and then naturally cooled to room temperature to obtain a sodium-ion battery modified anthracite-based hard carbon electrode material, denoted as GA0.1. In this step, during the low-temperature heat treatment stage, glucose molecules undergo chemical reactions such as dehydration condensation with oxygen-containing groups on the surface of anthracite. This in-situ modification strategy can block active defects in the anthracite structure, reduce the violent gas escape in the subsequent high-temperature stage, and inhibit the generation of physical defects from the source, thereby significantly improving the initial coulombic efficiency of the material. After grafting and repair, the anthracite is transformed into a highly disordered hard carbon structure at high temperature. The grafted organic molecules play a structural support role in the carbonization process, expanding the carbon interlayer spacing and providing a wider transport channel for the rapid insertion / extraction of sodium ions.

[0030] Example 2: This example differs from Example 1 in that glucose is replaced with sucrose (SA). The other steps and parameters are the same as in Example 1, resulting in a sodium-ion battery modified anthracite-based hard carbon electrode material.

[0031] Example 3: This example differs from Example 1 in that glucose is replaced with cellulose (CA). The other steps and parameters are the same as in Example 1, resulting in a sodium-ion battery modified anthracite-based hard carbon electrode material.

[0032] Example 4: This example differs from Example 1 in that glucose is replaced with lignin (LA), while the other steps and parameters are the same as in Example 1, resulting in a sodium-ion battery modified anthracite-based hard carbon electrode material.

[0033] Figure 1 The XRD patterns of the original anthracite carbon material and the hard carbon products obtained by modifying it with glucose (GA), sucrose (SA), cellulose (CA), and lignin (LA) in Examples 1-4 show that all samples exhibit two distinct broad diffraction peaks near 24° and 43°, corresponding to the (002) and (100) crystal planes of hard carbon, respectively. This indicates that after high-temperature carbonization, both anthracite and its modified products were successfully transformed into a typical amorphous hard carbon structure. The broad peak shape indicates that the material consists of highly disordered, randomly stacked carbon layers. Compared with the samples directly carbonized from the original anthracite, the modified samples show a clear trend of shifting the (002) peak position to a lower angle, corresponding to the interplanar spacing d. 002 The increase in specific capacity is due to the fact that small organic molecules act as "pillars" between anthracite microcrystals during grafting and carbonization, preventing the microcrystals from tightly stacking at high temperatures, which is beneficial to improving the specific capacity and rate performance of the material.

[0034] Figure 2 A comparison of the Raman spectra of the original anthracite carbon material and the modified anthracite-based hard carbon electrode materials for sodium-ion batteries obtained by adding glucose (GA), sucrose (SA), cellulose (CA), and lignin (LA) in Examples 1-4 was conducted. All samples showed Raman spectra at 1350 cm⁻¹. -1 (D-band, representing disordered defects) and 1580 cm -1 The G band (representing the degree of graphitization) exhibits a significant characteristic peak, and the intensity ratio of the two bands is an important indicator of the degree of disorder in the carbon matrix. The ratio of GA in the modified sample (0.94) is significantly lower than that of the original anthracite (1.07). Glucose organic molecules, through low-temperature grafting, can capture and repair active defects and unstable sites on the anthracite surface in situ, reducing the generation of physical defects during carbonization and thus improving the material's initial coulombic efficiency. In contrast, the intensity ratio of the D band to the G band characteristic peaks in the sucrose (SA) and lignin (LA) modified products is greater than that of the original anthracite (1.07). This indicates that the sucrose (SA) and lignin (LA) modified products introduce more structural defects or disordered carbon during pyrolysis, relatively increasing the degree of disorder in the material. The higher content of structural defects increases the active sites for electrolyte decomposition reactions, leading to increased irreversible capacity loss during SEI film formation, thereby reducing the material's initial coulombic efficiency.

[0035] Electrodes were prepared using the original anthracite carbon material and the sodium-ion battery modified anthracite-based hard carbon electrode materials obtained in Examples 1-4 by adding glucose, sucrose, cellulose, and lignin. Specifically, 600 mg of negative electrode material, 75 mg of sodium carboxymethyl cellulose, and 75 mg of conductive carbon black were accurately weighed into a brown glass bottle, and 2.5 mL of H2O was added as a solvent. The mixture was stirred at room temperature for 24 h until homogeneous. The resulting slurry was then uniformly coated onto a Cu foil with a thickness of 11 µm, resulting in a coating thickness of 100 µm and an active material loading of 2 mg / cm³. -2 The coated copper foil was transferred to a vacuum drying oven at 80 °C and dried for 12 h. It was then cut into electrode discs with a diameter of 12 mm and assembled into a half-cell. A sodium metal disc was used as the counter electrode, and the electrolyte was a 1 mol / L NaPF6 dimethyl ether (DME) solution, with a volume of 160 μL. The assembled cell was then subjected to a 1 A g... -1The battery was cycled 1000 times at a specific current density. The specific test steps were: constant current charging, rest, constant current discharging, rest, cycling, and termination. The battery was first activated by cycling 3 times at a low current density of 0.1C, and then subjected to cycle charge-discharge tests at a specific current density, with a test voltage range of 0.01–2 V. The cycle performance after 1000 cycles at a current density of 1 A / g is shown in Table 1. As can be seen from Table 1, glucose has the best improvement effect on the performance of anthracite-based carbon materials. The modified carbon materials have a lower defect density, which greatly improves the first-cycle coulombic efficiency of the original anthracite. The moderate interlayer spacing allows it to maintain a complete disordered structure during battery cycling while having a high capacity, making it less prone to structural collapse. Even after 1000 long cycles, it still has a high capacity retention rate, and its overall performance is excellent.

[0036] Table 1 Comparison of Cyclic Performance of Different Modifiers

[0037] sample Modifier Initial specific capacity (mAh / g) First-lap coulomb efficiency (%) Capacity retention rate (%) anthracite 202 74 79 Example 1 glucose 252 81 83 Example 2 sucrose 145 70 81 Example 3 Cellulose 167 76 80 Example 4 Lignin 184 75 75

[0038] Figure 3 The images show the infrared spectra of raw glucose, raw anthracite, and the glucose-modified anthracite precursor from the low-temperature heat treatment stage in Example 1. In the spectrum of raw glucose, at 3400 cm⁻¹... -1 A strong -OH vibration peak was present nearby, but the intensity of this -OH peak was significantly weakened in the precursor sample after low-temperature treatment at 400 °C. Meanwhile, the glucose-modified anthracite precursor showed a peak intensity of 1386 cm⁻¹. -1 A distinct new peak appeared at the point, which corresponds to the vibration of the ester group (O=C-OR). Since the original anthracite does not have a similar feature at this point, the appearance of this new peak proves that an esterification reaction has occurred between the hydroxyl group in the glucose molecule and the carboxyl group on the surface of the anthracite. This ensures that the glucose molecule can be anchored in situ on the coal-based skeleton and accurately repair defects during the subsequent high-temperature carbonization process.

[0039] Figure 4 The XPS images of anthracite-based hard carbon and glucose-modified anthracite-based hard carbon in Example 1 are shown. Peak convolution fitting analysis was performed on the C1s high-resolution spectra, mainly including sp... 2 C, sp 3 C peaks and oxygen-containing functional group peaks for CO and C=O. In hard carbon materials, sp 3 The carbon content typically reflects the defect density of the carbon layer. The sp content of pristine anthracite-based carbon materials... 3 C and sp 2 The C peak area ratio was 0.471, while this ratio significantly decreased to 0.389 in the sample after in-situ modification with glucose molecules. 3The significant decrease in C content directly demonstrates that the modified hard carbon material has a lower defect density, a result consistent with the trend of ratio changes in the Raman spectrum. Due to the reduction in defect sites, irreversible side reactions of the electrolyte on the material surface and irreversible capture of sodium ions are effectively suppressed, resulting in a significant improvement in the first coulombic efficiency.

[0040] Example 5: This example differs from Example 1 in that the mass ratio of anthracite powder to modifier glucose (GA) in step one is 95:5; the other steps and parameters are the same as in Example 1, and the resulting sodium-ion battery modified anthracite-based hard carbon electrode material is denoted as GA0.05.

[0041] Example 6: This example differs from Example 1 in that the mass ratio of anthracite powder to modifier glucose (GA) in step one is 70:30; the other steps and parameters are the same as in Example 1, and the resulting sodium-ion battery modified anthracite-based hard carbon electrode material is denoted as GA0.3.

[0042] Figure 5 The XRD patterns of the samples prepared in Examples 1 and 5-6, as well as glucose and anthracite, are shown in the figures. It can be seen that as the glucose addition ratio increases from 5% to 30%, the (002) characteristic diffraction peak of the hard carbon material exhibits a significant and continuous shift to lower angles. According to the Bragg equation, the original anthracite has the smallest interlayer spacing, which gradually increases with the increase of the modifier ratio. This proves that the glucose modifier plays a significant layer-expanding role in the carbonization process, effectively reducing the kinetic barrier to sodium ion insertion and facilitating Na+ intercalation. + It provides more storage space.

[0043] Figure 6 The Raman spectra of the samples prepared in Examples 1 and 5-6 are shown below. Figure 6 It can be seen that as the amount of glucose added is adjusted, the degree of defect in the material first increases and then decreases. The GA0.1 sample shows the lowest defect density, which indicates that glucose molecules can fill the active defect sites in the anthracite structure through esterification reaction, play an in-situ repair role, help reduce the irreversible side reactions of the electrolyte on the surface, and thus obtain higher initial coulombic efficiency and better cycle stability.

[0044] Electrodes were prepared using the sodium-ion battery modified anthracite-based hard carbon electrode materials prepared in Examples 1 and 5-6. Specifically, 600 mg of negative electrode material, 75 mg of sodium carboxymethyl cellulose, and 75 mg of conductive carbon black were accurately weighed into a brown glass bottle. 2.5 mL of H2O was added as a solvent, and the mixture was stirred at room temperature for 24 h until homogeneous. The resulting slurry was then uniformly coated onto a 11 µm thick Cu foil, resulting in a coating thickness of 100 µm and an active material loading of 2 mg / cm³. -2 The coated copper foil was transferred to a vacuum drying oven at 80 °C and dried for 12 h. It was then cut into electrode discs with a diameter of 12 mm and assembled into a half-cell. A sodium metal disc was used as the counter electrode. The electrolyte was a 1 mol / L dimethyl ether (DME) solution of NaPF6, with a volume of 160 μL. The assembled cell was then subjected to a 1 A g... -1 The battery was cycled 1000 times at a specific current density. The specific test steps were: constant current charging, rest, constant current discharging, rest, cycling, and termination. The battery was first activated by cycling 3 times at a low current density of 0.1C, and then subjected to cycle charge-discharge tests at a specific current density. The voltage range of the test was 0.01–2 V. Table 2 shows the electrochemical performance of the samples prepared in Examples 1 and 5–6.

[0045] Table 2 Comparison of recycling performance of anthracite-based hard carbon with different glucose addition levels

[0046] sample The amount of modifier added Initial specific capacity (mAh / g) First-lap coulomb efficiency (%) Capacity retention rate (%) anthracite 202 74 79 Example 5 GA0.05 227 79 83 Example 1 GA0.1 252 81 83 Example 6 GA0.3 210 73 82

[0047] As shown in Table 2, with the increase of glucose doping, the sodium storage performance of the materials exhibits a clear trend of first increasing and then decreasing. GA0.1 shows the best overall electrochemical activity, with the initial specific capacity of the GA0.1 sample reaching a maximum of 252 mAh / g, an increase of approximately 25% compared to the original anthracite's 202 mAh / g. Simultaneously, its initial coulombic efficiency significantly improved from 74% in the original anthracite to 81%. Furthermore, GA0.1 demonstrates superior cycle stability, with capacity retention increasing from 79% in the original sample to 83%. However, when the glucose addition increases further, the material's performance declines significantly. The initial specific capacity of GA0.3 drops to 210 mAh / g, and the initial coulombic efficiency falls to as low as 73%, even lower than that of unmodified anthracite. This indicates that GA0.1 represents a key performance inflection point; appropriate glucose doping can effectively stimulate the sodium storage potential of anthracite-based hard carbon, improving charge-discharge efficiency and cycle framework stability, while excessive addition inhibits electrochemical performance.

[0048] Example 7: This example differs from Example 1 in that in step one, the anthracite powder that has undergone impurity removal treatment is mixed with the modifier glucose (GA) at a mass ratio of 90:10 and then manually ground in a mortar for 1 hour to obtain the original carbon source; the other steps and parameters are the same as in Example 1.

[0049] Example 8: This example differs from Example 1 in that in step one, the anthracite powder that has undergone impurity removal treatment is mixed evenly with the modifier glucose (GA) at a mass ratio of 90:10, and then placed in a ball mill. The mixture is ball-milled for 6 hours at a ball-to-material mass ratio of 10:1 and a rotation speed of 300 rpm to obtain the original carbon source. Other steps and parameters are the same as in Example 1.

[0050] Example 9: This example differs from Example 1 in that in step one, the anthracite powder that has undergone impurity removal is added to deionized water and ultrasonically dispersed for 30 min to obtain a uniform suspension; then, according to the mass ratio of anthracite powder to modifier glucose (GA) of 90:10, glucose is added to the anthracite suspension, magnetically stirred at room temperature for 6 h, and then transferred to an 80 ℃ vacuum drying oven for drying for 12 h to obtain a uniformly impregnated original carbon source; other steps and parameters are the same as in Example 1.

[0051] The sodium-ion battery modified anthracite-based hard carbon electrode materials prepared in Examples 7-9 and 1 were subjected to scanning electron microscopy (SEM) testing, and the resulting images are shown below. Figure 7 As shown, (a) is the hand milling method of Example 7, (b) is the ball milling method of Example 8, (c) is the solution method of Example 9, and (d) is the tableting method of Example 1. Figure 7 It can be seen that the hand-milled sample mainly consists of large anthracite particles with only a few scattered glucose fragments adhering to the surface. There is a lack of effective interfacial contact between the components, exhibiting a clear phase separation state, which is not conducive to the synergistic evolution of the structure during heat treatment. Ball milling produced a large number of irregular small fragments and fresh fracture surfaces. Although this method increases the contact area, excessive structural destruction easily leads to too many surface defects and active sites, explaining its lower initial coulombic efficiency in subsequent tests. The solution-mixed particle surface exhibits a distinct "wrinkled" coating feature, originating from the recrystallization coating of glucose during solvent evaporation. While this method improves the uniformity of component distribution, the resulting coating layer is often relatively loose, with limited interfacial bonding. The tableting method exhibits the most significant lamellar structure feature. The anthracite particles are further compacted along their natural cleavage planes, while glucose molecules are forcefully squeezed into the gaps in the carbon layer, forming a dense morphology resembling "layers stacked."

[0052] The sodium-ion battery modified anthracite-based hard carbon electrode materials prepared in Examples 7-9 and 1 were used as negative electrode materials to prepare electrodes. Specifically, 600 mg of the negative electrode material, 75 mg of sodium carboxymethyl cellulose, and 75 mg of conductive carbon black were accurately weighed into a brown glass bottle, and 2.5 mL of H2O was added as a solvent. The mixture was stirred at room temperature for 24 h until homogeneous. The obtained slurry was then uniformly coated onto a Cu foil with a thickness of 11 µm, resulting in a coating thickness of 100 µm and an active material loading of 2 mg / cm³. -2 The coated copper foil was transferred to a vacuum drying oven at 80 °C and dried for 12 h. It was then cut into electrode discs with a diameter of 12 mm and assembled into a half-cell. A sodium metal disc was used as the counter electrode, and the electrolyte was a 1 mol / L NaPF6 dimethyl ether (DME) solution, with a volume of 160 μL. The assembled cell was then subjected to a 1 A g... -1 The battery was cycled 1000 times at a specific current density. The specific test steps were: constant current charging, rest, constant current discharging, rest, cycling, and termination. The battery was first activated by cycling 3 times at a low current density of 0.1C, and then subjected to cycle charge-discharge tests at a specific current density, with a test voltage range of 0.01–2 V. The obtained electrochemical cycle performance is shown in Table 3.

[0053] Table 3 Comparison of Glucose / Anthracite Hard Carbon Cycling Performance with Different Mixing Methods

[0054] sample Mixing method Initial specific capacity (mAh / g) First-lap coulomb efficiency (%) Capacity retention rate (%) Example 7 Hand grinding method 162 77 79 Example 8 Ball milling method 189 70 73 Example 9 solution method 223 81 85 Example 1 Tableting method 252 81 83

[0055] As shown in Table 3, the tableting method has a significant advantage in improving sodium storage capacity. The sample prepared by this method exhibits the highest initial specific capacity, reaching 252 mAh / g, which is approximately 13%, 33%, and 55% higher than the solution method, ball milling method, and hand milling method, respectively. Regarding the initial coulombic efficiency, both the tableting and solution methods achieved the highest value of 81%, while the ball milling method had the lowest initial efficiency at only 70%. This may be attributed to the mechanical damage to the carbon skeleton caused by high-energy ball milling, resulting in more irreversible active sites. In terms of cycle stability, the solution method and tableting method showed better capacity retention, with capacity retention rates of 85% and 83%, respectively. In contrast, the ball milling and hand milling methods showed poor cycle stability, with retention rates of only 73% and 79%, respectively. In summary, by achieving optimal physical integration between precursors, the tableting process not only greatly stimulates the sodium storage potential of the material but also ensures excellent initial charge-discharge efficiency and cycle skeleton stability, making it the best preparation method among the four processes.

Claims

1. A method for preparing a modified hard carbon electrode material based on anthracite for sodium-ion batteries, characterized by, This method is performed in the following steps:

1. Mix the purified anthracite powder with the modifier until homogeneous to obtain the original carbon source; 2. The original carbon source is placed in a furnace and heated to 300-500 ℃ at a heating rate of 1-10 ℃ / min under inert gas protection, and held for 1-3 h to obtain a modified anthracite precursor; then, it is heated to 1000-1400 ℃ under a protective atmosphere and held for 1-3 h, and then naturally cooled to room temperature to obtain a sodium-ion battery modified anthracite-based hard carbon electrode material.

2. The method for preparing a modified hard carbon electrode material based on sodium-ion battery smokeless coal according to claim 1, characterized in that, The impurity removal process described in step one is as follows: Anthracite powder is added to a hydrochloric acid solution with a concentration of 4-4.5 mol / L, and magnetically stirred for 8-9 hours. Then, it is thoroughly washed with deionized water until the filtrate is neutral. Next, it is placed in a vacuum drying oven at a temperature of 75-80 ℃ and dried for 10-12 hours. The dried anthracite powder is then transferred to a hydrofluoric acid solution with a mass percentage concentration of 4%-5%, magnetically stirred for 2-3 hours, and then placed in a vacuum drying oven at a temperature of 75-80 ℃ and dried for 10-12 hours to complete the impurity removal process.

3. The method for preparing a modified hard carbon electrode material of sodium-ion battery based on anthracite according to claim 1 or 2, characterized in that, The modified material mentioned in step one is glucose, sucrose, cellulose, or lignin.

4. The preparation method of a sodium-ion battery modified hard carbon electrode material based on anthracite according to claim 1 or 2, characterized in that, The mass ratio of anthracite to modifier mentioned in step one is (1~19):

1.

5. The method for preparing a modified hard carbon electrode material of sodium-ion battery based on anthracite according to claim 1 or 2, characterized in that, The mixing method for anthracite and modifier mentioned in step one is ball milling, manual grinding, tableting, or solution impregnation.

6. The method for preparing a modified hard carbon electrode material of sodium-ion battery based on anthracite according to claim 5, characterized in that, The aforementioned tableting method involves: placing anthracite powder and a modifier into an agate mortar and grinding them thoroughly for 20-30 minutes to achieve initial uniform mixing; then transferring the mixed powder into a mold, applying a pressure of 20-22 MPa on a tablet press and holding it for 2 minutes, demolding and removing it to obtain a round, flat original carbon source.

7. The method for preparing a modified hard carbon electrode material of sodium-ion battery based on anthracite according to claim 5, characterized in that, The solution impregnation method is as follows: anthracite powder is added to deionized water and ultrasonically dispersed for 30 min to obtain a uniform suspension; then the modifier is added to the anthracite suspension, magnetically stirred at room temperature for 5-6 h, and then transferred to a vacuum drying oven at 75-80 ℃ to dry for 10-12 h to obtain the original carbon source after uniform impregnation.

8. The method for preparing a modified hard carbon electrode material of sodium-ion battery based on anthracite according to claim 1 or 2, characterized in that, The inert gas mentioned in step two is argon, nitrogen, or carbon dioxide.

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