Sodium ion battery hard carbon negative electrode material and preparation method thereof

Abstract

The application belongs to the technical field of sodium ion batteries, and particularly relates to a sodium ion battery hard carbon negative electrode material taking bamboo and coal tar as precursors and a preparation method thereof. The method is prepared through two-step processes of air pre-oxidation and high-temperature carbonization, and utilizes the liquid-solid composite synergistic effect of the coal tar and the bamboo: the aromatic components in the coal tar fill the surface defects and excessive pores of the bamboo in the carbonization process, reduce the specific surface area, and reduce the irreversible capacity loss; meanwhile, a similar bonding bridge structure is constructed on the surface of the carbon skeleton, the structural stability is enhanced, and the cycle pulverization is inhibited. The obtained material significantly improves the initial coulombic efficiency, the cycle life and the tap density, and is suitable for large-scale production due to the wide source of raw materials and low cost.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a hard carbon anode material for sodium-ion batteries using coal tar and bamboo as precursors and its preparation method. Background Technology

[0002] With the global energy crisis and environmental pollution becoming increasingly severe, developing low-cost, highly safe, large-scale energy storage technologies has become a key path to achieving the "dual carbon" goal. Sodium-ion batteries are considered an ideal choice for next-generation large-scale energy storage systems due to the abundance and wide distribution of sodium resources, low cost, and strong compatibility with lithium-ion battery manufacturing processes. In the key material system of sodium-ion batteries, hard carbon, due to its unique amorphous carbon microstructure, large carbon interlayer spacing (usually greater than 0.37 nm), abundant defect sites and microporous structure, can reversibly insert sodium ions and provide a considerable sodium storage capacity of 300-400 mAh / g. At the same time, its low sodium storage potential is conducive to improving the energy density of the whole cell, and it has become the most widely used anode material for commercial sodium-ion batteries. The electrochemical performance of hard carbon materials is highly dependent on the chemical composition and microstructure of the precursors. Currently, hard carbon precursors mainly fall into three categories: resin-based (e.g., phenolic resins, epoxy resins), biomass-based (e.g., coconut shells, straw, wood), and fossil fuel-based (e.g., coal tar pitch, petroleum pitch). Among these, biomass precursors are considered the most promising source for large-scale hard carbon applications due to their renewability, wide availability, low cost, and rich content of heteroatoms such as nitrogen, oxygen, and sulfur. They also naturally possess a hierarchical porous structure and a large specific surface area, which is beneficial for electrolyte wetting and rapid ion transport. Among numerous biomass raw materials, bamboo exhibits unique advantages. Moso bamboo, belonging to the genus *Phyllostachys* of the Poaceae family, is the most widely distributed and largest-volume bamboo species in my country, mainly concentrated in southern provinces such as Fujian, Jiangxi, Zhejiang, and Hunan, accounting for over 50% of the global planting area. Moso bamboo has an extremely rapid growth rate, reaching maturity in 3-5 years, with an annual biomass yield of 20-40 tons / hectare, far superior to fast-growing trees (5-10 tons / hectare). Furthermore, it requires no replanting after harvesting, as new bamboo shoots sprout from underground rhizomes, making it a truly renewable resource. From a cost perspective, the price of moso bamboo raw material is only 200-400 yuan / ton, far lower than coconut shell (2000-3000 yuan / ton) and phenolic resin (8000-12000 yuan / ton). In terms of chemical composition, moso bamboo is rich in cellulose, hemicellulose and lignin. This comprehensive polysaccharide-aromatic polymer system is easy to form an amorphous carbon structure with abundant defects and moderate interlayer spacing after high-temperature carbonization. At the same time, moso bamboo naturally has a unique vascular bundle-thin-wall cell multi-level pore structure, which is conducive to the construction of a rapid electron / ion conduction network. In addition, the silicon element inherent in moso bamboo can form silicon oxide nanoparticles in situ during carbonization, which play a role in pore formation and support, further enhancing the sodium storage active sites. However, practical applications show that hard carbon materials prepared solely from bamboo-based biomass precursors suffer from the following insurmountable defects: First, low initial coulombic efficiency, mainly due to the large specific surface area of ​​bamboo biomass-based hard carbon and the presence of numerous oxygen-containing functional groups on its surface, leading to the formation of excessive solid electrolyte interfacial films and irreversible side reactions during the initial charge-discharge process; second, insufficient long-cycle stability, as the low mechanical strength of biomass-derived hard carbon makes it prone to microstructural collapse and pulverization during repeated sodium ion insertion / extraction; third, low tap density, limiting the volumetric energy density of the battery; and fourth, poor batch stability, as the chemical composition of different batches of bamboo fluctuates significantly due to factors such as origin, season, and growth environment, making it difficult to guarantee the consistency of the final carbon material performance and limiting its large-scale industrial application. Coal tar, a byproduct of coal dry distillation or pyrolysis, can be classified into high-temperature coal tar and low-temperature coal tar based on the distillation temperature. High-temperature coal tar is rich in polycyclic aromatic hydrocarbons (PAHs), such as naphthalene, anthracene, and phenanthrene, with a content reaching up to 50%. It has high aromaticity, a carbon content typically greater than 90%, and low ash content. During carbonization, it readily forms a highly ordered graphitic microcrystalline structure, exhibiting excellent electronic conductivity and structural stability. However, when used alone as a hard carbon precursor, the interlayer spacing of high-temperature coal tar is often less than 0.36 nm, which is unfavorable for sodium ion diffusion. Low-temperature coal tar contains a higher proportion of aliphatic side chains and phenolic compounds, with a moderate degree of cross-linking. During carbonization, it retains more amorphous carbon regions and defect sites. However, its residual carbon content is relatively low, and its viscosity is high, making it difficult to process alone. Summary of the Invention

[0003] To overcome the limitations of a single precursor, bamboo-based biomass can be composite-modified with coal tar. The combination of coal tar and biomass can achieve a liquid-solid synergistic effect: on the one hand, the aromatic components in coal tar can fill surface defects and overdeveloped pores in bamboo-based biomass during carbonization, effectively reducing specific surface area, minimizing irreversible capacity loss, and improving initial coulombic efficiency; on the other hand, coal tar can coat or construct "bonding bridges" on the surface of the carbon skeleton of bamboo-based biomass, enhancing the material's mechanical strength and structural stability, and inhibiting pulverization during recycling; furthermore, the high carbon content in coal tar can increase the overall char yield, compensating for the low carbon production rate of bamboo-based biomass, while simultaneously adjusting the interlayer spacing of the final carbon material to a suitable range, optimizing sodium ion storage kinetics. However, there is no existing research on the preparation of hard carbon anodes using bamboo and coal tar composites. Therefore, developing a high-performance composite hard carbon anode material based on bamboo and coal tar and its preparation process by fully leveraging the synergistic effect of the solid-liquid interface of amorphous carbon microstructures with high-temperature / low-temperature coal tar and bamboo as the substrate, and by utilizing the compatibility of the interface, is of significant scientific importance and application value for promoting the large-scale industrialization of sodium-ion batteries. To achieve the above objectives, the technical solution of the present invention is as follows: A hard carbon anode material for sodium-ion batteries and its preparation method are disclosed. The material is prepared from bamboo-based biomass material and high-temperature coal tar / low-temperature coal tar. The specific steps are as follows: (1) Wash the bamboo to remove dust and other impurities, and dry it in a constant temperature oven at 70℃ for 24 h to obtain clean and dry biomass material; (2) Place the material in a crucible and send it into the furnace, and set the heating conditions: 2 ~ 6℃ min. -1 The furnace is heated at a rate that raises the temperature from room temperature to 150-350℃, and maintained at this temperature for 8-16 hours. Then, it is cooled down at a rate of 2-6℃ / min until it returns to room temperature. The pre-oxidized material is then removed. (3) Grind and knead the pre-oxidized material using an agate mortar to obtain a pre-oxidized material powder with bamboo as the base material. Weigh a certain mass of the above powder and grind and knead it with coal tar in different mass ratios. After thorough mixing, add it to a crucible and push it into the center of the heating tube of a tube furnace. Add a furnace plug, connect the gas cylinder, and ensure good sealing inside the tube. Open the valve of the argon cylinder and introduce argon gas into the furnace, adjusting the gas flow rate to 50-300 mL / min. Set the heating program: heat at a heating rate of 1-120℃ / min to raise the furnace temperature from room temperature to 1000-1600℃, maintain the heating for 2-5 h, and then cool down to room temperature at a cooling rate of 2-10℃ / min. After heating, a hard carbon material with coal tar and bamboo as the base material is obtained. Preferably, in step (2), the heating rate is 3 ~ 5℃ / min during heating and the cooling rate is 3 ~ 5℃ / min during cooling. Preferably, in step (2), the heating temperature is 200-300℃. Preferably, in step (2), the heating time is 11-13 h. Preferably, in step (3), the heating rate is 3 ~ 50℃ / min during heating and the cooling rate is 3 ~ 5℃ / min during cooling. Preferably, in step (3), the heating temperature is 1100-1300℃. Preferably, in step (3), the heating time is 2-4 hours. Preferably, in step (3), the flow rate of the introduced argon gas is 100-200 mL / min. A sodium-ion battery uses an electrode made of hard carbon material based on coal tar and bamboo as the negative electrode. Beneficial effects my country has abundant bamboo production, making it suitable as a raw material for large-scale production of hard carbon. This invention provides a sodium-ion battery hard carbon anode material using coal tar and bamboo as precursors, prepared through a two-stage sintering process of air pre-oxidation and high-temperature sintering in an inert atmosphere. The process involves air pre-oxidation to remove volatile components from bamboo-based biomass materials, increasing porosity and specific surface area. By leveraging the synergistic effect of coal tar and bamboo-based biomass liquid-solid composite, the aromatic components in coal tar promote cross-linking reactions between biomass molecules and aromatic components in coal tar during the carbonization process of bamboo-based biomass. This regulates the types, composition, and distribution of surface functional groups, as well as the pore structure, filling surface defects and overdeveloped pores, effectively reducing specific surface area, minimizing irreversible capacity loss, and improving initial coulombic efficiency. Furthermore, coal tar coats or constructs "bonding bridges" on the surface of the bamboo-based biomass carbon skeleton, enhancing the material's mechanical strength and structural stability, inhibiting microstructure collapse and pulverization during repeated sodium ion insertion / extraction in cycling, and improving cycle life. The high carbon content in coal tar increases overall hard carbon yield, compensating for the low carbon yield of bamboo-based biomass, while also regulating the interlayer spacing and pore structure of the final carbon material, thus increasing the battery's volumetric energy density. This invention uses bamboo and coal tar as raw materials, making full use of the characteristics of high cellulose, hemicellulose and lignin content in bamboo structure, the unique vascular bundle-thin-wall cell multi-level pore structure, and the uniform components of coal tar as fossil fuel, neutralizing the natural volatility of biomass, and improving the capacity and cycle stability of sodium-ion batteries. Attached Figure Description Figure 1 The image shows a scanning electron microscope (SEM) image of the bamboo-low-temperature coal tar composite hard carbon BHC-L-55-1150 prepared in Example 1. Figure 2 shows the X-ray powder diffraction (XRD) crystal pattern of bamboo-low-temperature coal tar composite hard carbon BHC-L-55-1150 prepared in Example 1. Figure 3 shows the capacity-voltage diagram of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-55-1150-PVDF prepared in Example 1 after 3 cycles at 0.1 C in a sodium-ion battery. Figure 4 shows the capacity-voltage diagram of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-73-1150-PVDF prepared in Example 2 after 3 cycles at 0.1 C in a sodium-ion battery. Figure 5 shows the capacity-voltage diagram of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-55-1150-PVDF prepared in Example 3 after 3 cycles at 0.1 C in a sodium-ion battery. Figure 6 shows the capacity-voltage diagram of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-37-1150-PVDF prepared in Example 4 after 3 cycles at 0.1 C in a sodium-ion battery. Figure 7 shows the capacity-voltage diagram of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-73-1150-PVDF prepared in Example 5 after 3 cycles at 0.1 C in a sodium-ion battery. Figure 8 shows the capacity-voltage diagram of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-37-1150-PVDF prepared in Example 6 after 3 cycles at 0.1 C in a sodium-ion battery. Figure 9 shows the capacity-voltage diagram of the bamboo biomass hard carbon electrode sheet BHC-1150-PVDF prepared in Comparative Example 1 after 3 cycles at 0.1 C in a sodium-ion battery. Figure 10 shows the cycle-capacity diagram of the rate performance of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-55-1150-PVDF prepared in Example 1 in a sodium-ion battery. Figure 11 shows the cycle-capacity graph of the rate performance of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-73-1150-PVDF prepared in Example 2 in a sodium-ion battery. Figure 12 shows the cycle-capacity graph of the rate performance of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-55-1150-PVDF prepared in Example 3 in a sodium-ion battery. Figure 13 shows the cycle-capacity diagram of the rate performance of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-37-1150-PVDF prepared in Example 4 in a sodium-ion battery. Figure 14 shows the cycle-capacity graph of the rate performance of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-73-1150-PVDF prepared in Example 5 in a sodium-ion battery. Figure 15 shows the cycle-capacity graph of the rate performance of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-37-1150-PVDF prepared in Example 6 in a sodium-ion battery. Figure 16 shows the cycle-capacity diagram of the rate performance of the bamboo biomass hard carbon electrode sheet BHC-1150-PVDF prepared in Comparative Example 1 in a sodium-ion battery. Figure 17 is a comparison of cycle-capacity-efficiency of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-55-1150-PVDF prepared in Example 1 after 50 cycles at 0.2 C in a sodium-ion battery. Figure 18 is a comparison of cycle-capacity-efficiency of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-73-1150-PVDF prepared in Example 2 after 50 cycles at 0.2 C in a sodium-ion battery. Figure 19 is a comparison of cycle-capacity-efficiency of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-55-1150-PVDF prepared in Example 3 after 50 cycles at 0.2 C in a sodium-ion battery. Figure 20 is a comparison of cycle-capacity-efficiency of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-37-1150-PVDF prepared in Example 4 after 50 cycles at 0.2 C in a sodium-ion battery. Figure 21 is a comparison of cycle-capacity-efficiency of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-73-1150-PVDF prepared in Example 5 after 50 cycles at 0.2 C in a sodium-ion battery. Figure 22 is a comparison of cycle-capacity-efficiency of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-37-1150-PVDF prepared in Example 6 after 50 cycles at 0.2 C in a sodium-ion battery. Figure 23 is a comparison of the cycle-capacity-efficiency of the bamboo biomass hard carbon electrode sheet BHC-1150-PVDF prepared in Comparative Example 1 after 50 cycles at 0.2 C in a sodium-ion battery. Figure 24 is a comparison of cycle-capacity-efficiency of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-55-1150-PVDF prepared in Example 1 after 200 cycles at 1 C in a sodium-ion battery. Figure 25 is a comparison of cycle-capacity-efficiency of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-73-1150-PVDF prepared in Example 2 after 200 cycles at 1 C in a sodium-ion battery. Figure 26 is a comparison of cycle-capacity-efficiency of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-55-1150-PVDF prepared in Example 3 after 200 cycles at 1 C in a sodium-ion battery. Figure 27 is a comparison of cycle-capacity-efficiency of the bamboo-high temperature coal tar composite hard carbon electrode sheet BHC-H-37-1150-PVDF prepared in Example 4 after 200 cycles at 1 C in a sodium-ion battery. Figure 28 is a comparison of cycle-capacity-efficiency of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-73-1150-PVDF prepared in Example 5 after 200 cycles at 1 C in a sodium-ion battery. Figure 29 is a comparison of cycle-capacity-efficiency of the bamboo-low-temperature coal tar composite hard carbon electrode sheet BHC-L-37-1150-PVDF prepared in Example 6 after 200 cycles at 1 C in a sodium-ion battery. Figure 30 is a comparison of the cycle-capacity-efficiency of the bamboo biomass electrode sheet BHC-1150-PVDF prepared in Comparative Example 1 after 200 cycles at 1C in a sodium-ion battery. Specific implementation methods The present invention will be further described in detail below with reference to specific embodiments. In the following embodiments or comparative examples: Assembly of the button cell: At room temperature, the working electrode was first prepared by mixing the material prepared in the examples or comparative examples with a conductive agent and a binder in a ratio of 8:1:1 and grinding it to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil with a doctor blade and dried in an oven at 100°C under vacuum for 12 h to obtain the working electrode. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm as the negative electrode using a die-casting machine, a 15.6 mm diameter sodium metal sheet as the counter electrode, a 1 M NaPF6 DME solution as the electrolyte solution, and a 19 mm diameter glass fiber disc as the separator. The button cell was then assembled in a glove box filled with an inert atmosphere. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30 ℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. Example 1 Take an appropriate amount of washed and dried bamboo, add it to a furnace pan and place it in the furnace chamber. Heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 250℃, maintain the heating for 12 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain a pre-oxidized material. Take an appropriate amount of pre-oxidized bamboo material and grind it into a fine powder. Then weigh the pre-oxidized bamboo material powder and low-temperature coal tar at a mass ratio of 5:5, grind and mix them thoroughly in an agate mortar, add them to a crucible, place it in the center of the heating tube of a tube furnace, introduce argon gas at a rate of 150mL / min, heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 1150℃, maintain the heating for 3 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain the hard carbon material BHC-L-55-1150. The BHC-L-55-1150 hard carbon material prepared in Example 1 of this invention was mixed with super-P conductive agent and PVDF binder in a ratio of 8:1:1 and ground to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil using a 100 μm doctor blade and vacuum dried in an oven at 100°C for 12 h to obtain the working electrode BHC-L-55-1150-PVDF. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm using a die-cutting machine as the negative electrode, a sodium metal sheet as the counter electrode, and a 1 M NaPF6 DME solution as the electrolyte solution. A button cell was assembled in an inert atmosphere glove box. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. The scanning electron microscope results of the material BHC-L-55-1150 are shown in Figure 1. The material exhibits an irregular sheet-like structure, with low-temperature coal tar forming an irregular cover on the original biomass structure surface. The X-ray powder diffraction crystal pattern of the material BHC-L-55-1150 is shown in Figure 2. Calculations show that the material... d 002 The interplanar spacing is approximately 0.4105 nm. Figure 3 shows the capacity-voltage diagram of the electrode BHC-L-55-1150-PVDF in a sodium-ion battery during the first three cycles at a charge-discharge rate of 0.1 C. The electrode exhibits a reversible specific capacity of 353.41 mAh / g at 0.1 C, with a low-voltage plateau capacity of 206.19 mAh / g, accounting for 58.34% of the total capacity, and a median voltage of 0.0928 V. This indicates that the material possesses excellent capacity performance while ensuring a large capacity output capability at low voltage. The rate performance test of the electrode BHC-L-55-1150-PVDF in a sodium-ion battery is shown in Figure 10. The electrode exhibits minimal capacity change as the current density gradually increases, and still maintains a capacity of 266.87 mAh / g at a high charge-discharge rate of 2 C. Furthermore, after recovering to a charge-discharge rate of 0.1 C, the capacity retention rate is 96.95%. These results demonstrate that the material exhibits excellent electron transport kinetics and structural stability. Figure 17 shows the cycle-capacity diagram of the BHC-L-55-1150-PVDF electrode in a sodium-ion battery at a charge-discharge rate of 0.2 C. After 50 cycles, it still possesses a high specific capacity of 333.26 mAh / g. Compared to the BHC-1150-PVDF electrode prepared in Comparative Example 1, BHC-L-55-1150-PVDF exhibits superior capacity performance, initial coulombic efficiency, and cycle stability. This demonstrates that the low-temperature coal tar and the addition of biomass hard carbon optimized the electron / ion transport kinetics, structural stability, and interfacial electrochemical stability, ultimately achieving a comprehensive improvement in comparative capacity, initial coulombic efficiency, and long cycle life. Finally, the material retains 94.63% of its capacity after 50 cycles at a charge-discharge rate of 0.2 C, proving its excellent cycle stability. Figure 24 shows the cycle-capacity diagram of the electrode BHC-L-55-1150-PVDF in a sodium-ion battery at a 1 C charge-discharge rate. After 150 cycles, it still has a specific capacity of 280.72 mAh / g and a retention rate of 87.34%. Example 2 Take an appropriate amount of washed and dried bamboo, add it to a furnace pan and place it in the furnace chamber. Heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 250℃, maintain the heating for 12 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain a pre-oxidized material. Take an appropriate amount of pre-oxidized bamboo material and grind it into a fine powder. Then weigh the pre-oxidized bamboo material powder and high-temperature coal tar at a mass ratio of 7:3, grind and mix them thoroughly in an agate mortar, add them to a crucible, place it in the center of the heating tube of a tube furnace, introduce argon gas at a rate of 150mL / min, heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 1150℃, maintain the heating for 3 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain the hard carbon material BHC-H-73-1150. The BHC-H-73-1150 hard carbon material prepared in Example 2 of this invention was mixed with super-P conductive agent and PVDF binder in a ratio of 8:1:1 and ground to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil using a 100 μm doctor blade and vacuum dried in an oven at 100°C for 12 h to obtain the working electrode BHC-H-73-1150-PVDF. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm using a die-cutting machine as the negative electrode, a sodium metal sheet as the counter electrode, and a 1 M NaPF6 DME solution as the electrolyte solution. A button cell was assembled in an inert atmosphere glove box. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. The prepared electrode BHC-H-73-1150-PVDF was tested in a sodium-ion battery, and... Figure 4 The electrode exhibits a reversible capacity of 299.83 mAh / g at a charge-discharge rate of 0.1 C, with a low-voltage plateau capacity of 152.46 mAh / g, a median voltage of 0.1166 V, and an initial coulombic efficiency of 74.52%. Figure 18 This electrode exhibits a reversible capacity of 258.29 mAh / g after 50 cycles at a 0.2 C charge-discharge rate, with a capacity retention of 91.55%. Figure 25 This electrode exhibits a reversible capacity of 231.32 mAh / g after 150 cycles at a 1 C charge-discharge rate, with a capacity retention of 94.53%. Figure 11In the rate performance test of this electrode, the capacity was 261.55 mAh / g at a high charge-discharge rate of 2 C, and the capacity retention rate was 97.13% after recovering to a charge-discharge rate of 0.1 C. Example 3 A suitable amount of washed and dried bamboo was added to a furnace pan and placed into the furnace chamber. The furnace temperature was increased from room temperature to 250°C at a heating rate of 3°C / min and maintained for 12 hours. Then, the temperature was reduced to room temperature at a cooling rate of 5°C / min to obtain the pre-oxidized material. A suitable amount of the pre-oxidized bamboo material was ground into a fine powder. Then, the pre-oxidized bamboo powder and high-temperature coal tar were weighed at a mass ratio of 5:5, thoroughly ground and mixed in an agate mortar, and added to a crucible. This crucible was then placed in the center of the heating tube of a tube furnace. Argon gas was introduced at a rate of 150 mL / min, and the furnace temperature was increased from room temperature to 1150°C at a heating rate of 3°C / min and maintained for 3 hours. Then, the temperature was reduced to room temperature at a cooling rate of 5°C / min to obtain the hard carbon material BHC-H-55-1150. The BHC-H-55-1150 hard carbon material prepared in Example 3 of this invention was mixed with super-P conductive agent and PVDF binder in a ratio of 8:1:1 and ground to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil using a 100 μm doctor blade and vacuum dried in an oven at 100°C for 12 h to obtain the working electrode BHC-H-55-1150-PVDF. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm using a die-cutting machine as the negative electrode, a sodium metal sheet as the counter electrode, and a 1 M NaPF6 DME solution as the electrolyte solution. A button cell was assembled in an inert atmosphere glove box. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. The prepared electrode BHC-H-55-1150-PVDF was tested in a sodium-ion battery, and... Figure 5 The electrode exhibits a reversible capacity of 273.36 mAh / g at a charge-discharge rate of 0.1 C, with a low-voltage plateau capacity of 137.48 mAh / g, a median voltage of 0.1239 V, and an initial coulombic efficiency of 59.70%. Figure 19This electrode exhibits a reversible capacity of 249.97 mAh / g after 50 cycles at a 0.2 C charge-discharge rate, with a capacity retention of 94.01%. Figure 26 The electrode exhibits a reversible capacity of 212.66 mAh / g after 150 cycles at a 1C charge-discharge rate, with a capacity retention of 88.02%. Figure 12 In the rate performance test of this electrode, the capacity was 213.46 mAh / g at a high charge-discharge rate of 2 C, and the capacity retention rate was 95.63% after recovering to a charge-discharge rate of 0.1 C. Example 4 Take an appropriate amount of washed and dried bamboo, add it to a furnace pan and place it in the furnace chamber. Heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 250℃, maintain the heating for 12 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain a pre-oxidized material. Take an appropriate amount of pre-oxidized bamboo material and grind it into a fine powder. Then weigh the pre-oxidized bamboo material powder and high-temperature coal tar at a mass ratio of 3:7, grind and mix them thoroughly in an agate mortar, add them to a crucible, place it in the center of the heating tube of a tube furnace, introduce argon gas at a rate of 150mL / min, heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 1150℃, maintain the heating for 3 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain the hard carbon material BHC-H-37-1150. The BHC-H-37-1150 hard carbon material prepared in Example 4 of this invention was mixed with super-P conductive agent and PVDF binder in a ratio of 8:1:1 and ground to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil using a 100 μm doctor blade and vacuum dried in an oven at 100°C for 12 h to obtain the working electrode BHC-H-37-1150-PVDF. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm using a die-cutting machine as the negative electrode, a sodium metal sheet as the counter electrode, and a 1 M NaPF6 DME solution as the electrolyte solution. A button cell was assembled in an inert atmosphere glove box. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. The prepared electrode BHC-H-37-1150-PVDF was tested in a sodium-ion battery, and... Figure 6The electrode exhibits a reversible capacity of 297.47 mAh / g at a charge-discharge rate of 0.1 C, with a low-voltage plateau capacity of 162.10 mAh / g, a median voltage of 0.1004 V, and an initial coulombic efficiency of 62.34%. Figure 20 This electrode exhibits a reversible capacity of 286.56 mAh / g after 50 cycles at a 0.2 C charge-discharge rate, with a capacity retention of 96.95%. Figure 27 This electrode exhibits a reversible capacity of 239.79 mAh / g after 150 cycles at a 1C charge-discharge rate, with a capacity retention of 89.00%. Figure 13 In the rate performance test, the capacity of this electrode was 248.20 mAh / g at a high charge-discharge rate of 2 C, and the capacity retention rate was 96.95% after recovering to a charge-discharge rate of 0.1 C. Example 5 Take an appropriate amount of washed and dried bamboo, add it to a furnace pan and place it in the furnace chamber. Heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 250℃, maintain the heating for 12 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain a pre-oxidized material. Take an appropriate amount of pre-oxidized bamboo material and grind it into a fine powder. Then weigh the pre-oxidized bamboo material powder and low-temperature coal tar at a mass ratio of 7:3, grind and mix them thoroughly in an agate mortar, add them to a crucible, place it in the center of the heating tube of a tube furnace, introduce argon gas at a rate of 150mL / min, heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 1150℃, maintain the heating for 3 hours, and then cool down to room temperature at a rate of 5℃ / min to obtain the hard carbon material BHC-L-73-1150. The BHC-L-73-1150 hard carbon material prepared in Example 5 of this invention was mixed with super-P conductive agent and PVDF binder in a ratio of 8:1:1 and ground to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil using a 100 μm doctor blade and vacuum dried in an oven at 100°C for 12 h to obtain the working electrode BHC-L-73-1150-PVDF. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm using a die-cutting machine as the negative electrode, a sodium metal sheet as the counter electrode, and a 1 M NaPF6 DME solution as the electrolyte solution. A button cell was assembled in an inert atmosphere glove box. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. The prepared electrode BHC-L-73-1150-PVDF was tested in a sodium-ion battery, and... Figure 7 The electrode exhibits a reversible capacity of 282.21 mAh / g at a charge-discharge rate of 0.1 C, with a low-voltage plateau capacity of 162.29 mAh / g, a median voltage of 0.1014 V, and an initial coulombic efficiency of 65.88%. Figure 21 This electrode exhibits a reversible capacity of 276.02 mAh / g after 50 cycles at a 0.2 C charge-discharge rate, with a capacity retention of 97.83%. Figure 28 This electrode exhibits a reversible capacity of 268.98 mAh / g after 150 cycles at a 1C charge-discharge rate, with a capacity retention of 94.36%. Figure 14 In the rate performance test, the capacity of this electrode was 268.20 mAh / g at a high charge-discharge rate of 2 C, and the capacity retention rate was 97.63% after recovering to a charge-discharge rate of 0.1 C. Example 6 Take an appropriate amount of washed and dried bamboo, add it to a furnace pan and place it in the furnace chamber. Heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 250℃, maintain this temperature for 12 hours, and then cool it down to room temperature at a rate of 5℃ / min to obtain the pre-oxidized material. Grind an appropriate amount of the pre-oxidized bamboo material into a fine powder, and weigh the pre-oxidized material and low-temperature coal tar at a mass ratio of 3:7. Grind and mix the mixture thoroughly in an agate mortar, then add it to a crucible and place it in the center of the heating tube of a tube furnace. Heat at a rate of 150 mL / min. -1 Argon gas was introduced at a rate of 3°C / min to raise the furnace temperature from room temperature to 1150°C. The temperature was maintained for 3 hours and then lowered to room temperature at a rate of 5°C / min to obtain the hard carbon material BHC-L-37-1150. The BHC-L-37-1150 hard carbon material prepared in Example 6 of this invention was mixed with super-P conductive agent and PVDF binder in a ratio of 8:1:1 and ground to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil using a 100 μm doctor blade and vacuum dried in an oven at 100°C for 12 h to obtain the working electrode BHC-L-37-1150-PVDF. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm using a die-cutting machine as the negative electrode, a sodium metal sheet as the counter electrode, and a 1 M NaPF6 DME solution as the electrolyte solution. A button cell was assembled in an inert atmosphere glove box. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. The prepared electrode BHC-L-37-1150-PVDF was tested in a sodium-ion battery, and... Figure 8 The electrode exhibits a reversible capacity of 297.07 mAh / g at a charge-discharge rate of 0.1 C, with a low-voltage plateau capacity of 175.83 mAh / g, a median voltage of 0.0947 V, and an initial coulombic efficiency of 69.27%. Figure 22 This electrode exhibits a reversible capacity of 283.62 mAh / g after 50 cycles at a 0.2 C charge-discharge rate, with a capacity retention of 96.99%. Figure 29 This electrode exhibits a reversible capacity of 272.90 mAh / g after 150 cycles at a 1 C charge-discharge rate, with a capacity retention of 92.54%. Figure 15 In the rate performance test, the capacity of this electrode was 245.29 mAh / g at a high charge-discharge rate of 2 C, and the capacity retention rate was 96.79% after recovering to a charge-discharge rate of 0.1 C. Comparative Example 1 Take an appropriate amount of washed and dried bamboo, add it to a furnace pan and place it in the furnace chamber. Heat at a rate of 3℃ / min until the furnace temperature rises from room temperature to 250℃, maintain this temperature for 12 hours, and then cool it down to room temperature at a rate of 5℃ / min to obtain the pre-oxidized material. Take an appropriate amount of the pre-oxidized bamboo material, grind it thoroughly in an agate mortar, add it to a crucible, and place it in the center of the heating tube of a tube furnace. Heat at a rate of 150 mL / min. -1Argon gas was introduced at a rate of 3°C / min to raise the furnace temperature from room temperature to 1150°C. The temperature was maintained for 3 hours and then lowered to room temperature at a rate of 5°C / min to obtain the hard carbon material BHC-1150. The BHC-1150 hard carbon material prepared in Comparative Example 1 of this invention was mixed with super-P conductive agent and PVDF binder in a ratio of 8:1:1 and ground to prepare a uniform slurry. Then, the obtained slurry was uniformly coated onto copper foil using a 100 μm doctor blade and vacuum dried in an oven at 100°C for 12 h to obtain the working electrode BHC-1150-PVDF. Finally, the copper foil coated with the sample was pressed into a small disc with a diameter of 11 mm using a die-cutting machine as the negative electrode, a sodium metal sheet as the counter electrode, and a 1 M NaPF6 DME solution as the electrolyte solution. A button cell was assembled in an inert atmosphere glove box. Electrochemical performance testing was conducted under the monitoring of the Xinwei Battery testing system, with a test voltage range of 0.01 - 2.6 V, a test method of nominal capacity of 300 mAh / g, and a test temperature of 30℃. After four cycles at a charge-discharge rate of 0.1 C, the electrode material was cycled at charge-discharge rates of 0.2 C and 1 C to detect its capacity performance and cycle stability. The rate performance of the electrode material was then detected by cycling at charge-discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 0.1 C for five cycles each. The prepared electrode BHC-1150-PVDF was tested in a sodium-ion battery, and... Figure 9 The electrode exhibits a reversible capacity of 308.30 mAh / g at a charge-discharge rate of 0.1 C, with a low-voltage plateau capacity of 163.28 mAh / g, a median voltage of 0.0987 V, and an initial coulombic efficiency of 62.04%. Figure 23 The electrode exhibits a reversible capacity of 289.72 mAh / g after 50 cycles at a 0.2 C charge-discharge rate, with a capacity retention of 93.30%. Figure 30 This electrode exhibits a reversible capacity of 257.67 mAh / g after 150 cycles at a 1 C charge-discharge rate, with a capacity retention of 90.78%. Figure 16 In the rate performance test, the capacity of this electrode was 261.10 mAh / g at a high charge-discharge rate of 2 C, and the capacity retention rate was 96.13% after recovering to a charge-discharge rate of 0.1 C. In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A hard carbon anode for sodium-ion batteries using coal tar and bamboo as precursors, characterized in that, The material is prepared from bamboo and coal tar.

2. The bamboo variety mentioned in claim 1 refers to moso bamboo.

3. The coal tar according to claim 1 can be high-temperature coal tar or low-temperature coal tar.

4. The main components of the high-temperature coal tar according to claim 3 include polycyclic aromatic hydrocarbons and their derivatives such as benzene, naphthalene, anthracene, phenanthrene, carbazole, and fluorene, heterocyclic compounds such as quinoline and pyridine, and phenols.

5. The main components of the low-temperature coal tar according to claim 3 include phenols and their derivatives, long-chain alkanes and alkenes, and monocyclic / bicyclic aromatic hydrocarbons such as cyclohexane and alkylbenzenes.

6. The sodium-ion battery hard carbon anode material and its preparation method according to claim 1, characterized in that, It is prepared by the following method: (1) Simply break the bamboo into small pieces, wash and dry them, heat them in the air to 150-350 ℃, keep heating for 8-16 hours, and cool them down to room temperature at a certain rate to obtain bamboo pre-oxidized material. (2) Take the above bamboo pre-oxidation material and grind and mix it with high-temperature coal tar and low-temperature coal tar at different mass ratios to obtain bamboo-coal tar mixture material. (3) Place the above bamboo-coal tar mixture in a crucible, heat it to 1000-1600 °C under a nitrogen atmosphere, keep heating for 2-5 h, and then cool it to room temperature to obtain a sodium-ion battery hard carbon anode with coal tar and bamboo as precursors.

7. The negative electrode material according to claim 6, characterized in that, In steps (1) and (3), the heating rate is controlled at 1~80 ℃ / min; the cooling rate is controlled at 2~10 ℃ / min.

8. The negative electrode material according to claim 6, characterized in that, In step (2), the mass ratio of bamboo pre-oxidation material to coal tar is between 3:7 and 7:

3.

9. A sodium-ion battery, wherein an electrode made of a hard carbon material based on the above-mentioned coal tar and bamboo is used as the negative electrode material.

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